I'd say Araucaria araucana is probably marginally the hardiest (down to around -20°C, exceptionally a little lower), with some of the other South American podocarps and cypresses following close behind (Prumnopitys andina, Podocarpus nubigenus, Lepidothamnus fonkii, Pilgerodendron uviferum).

Of broadleaves, Nothofagus antarctica is the only southern hemisphere tree reliably hardy in Denmark (zone 7) and I think may have been successful into the warmer parts of zone 6 in Sweden. Araucaria araucana has been tried in Denmark on numerous occasions, with numerous provenances, and always gets killed sooner or later, though some have struggled on for 30-40 years or so before finally succumbing to a severe winter.

In theory, Lepidothamnus fonkii should be as hardy as Nothofagus antarctica (as both occur right down to the southern tip of land on S America), so it may not have been given adequate trial yet. But even if it does take zone 6/7 winters, I doubt it can cope with any continental summer heat at all, as Tierra del Fuego has cold summers.

Resin

So it looks like no Southern hemisphere conifer is hardier than zone 8 eh? And the ones that might be marginally zone 7 cold hardy aren't at all heat tolerant.

I find it a bit surprising that none of the Southern hemisphere conifers appear to grow at high altitudes in temperate latitudes. Kind of like in the Andes there appears to be no woody plants that have adapted to growing in the higher altitude colder areas(areas that regularly hit -17.8°C(0°F) or colder for instance) that many Northern hemisphere woody plants have easily adapted to. It looks like there are large areas of higher altitude cold areas in the Andes which lack any woody plants.

OK, so a follow up, what's the most cold hardy Podocarpaceae?

I'm expirementing with growing Phyllocladus alpinus and Lagarostrobos franklinii as potted plants here in a very continental climate. They haven't seemed to be too negatively affected by the heat yet. I keep them above 20F/-6C in winter though. I recently got a Saxegothaea conspicua but it hasn't had to deal with a summer yet. I would love to try Lepidothamnus fonkii.
There is a reference to Podocarpus salignus being hardy to -13F/-25C; that was from Wikipedia the reference cited was: Huxley. A. The New RHS Dictionary of Gardening. I would be concerned about heat tolerance in a humid continental climate though.

That's very interesting eukaryote. Do you think you'll ever try and plant one out in a very protected micro-climate?

So, nobody else has any ideas of the most cold hardy Southern hemisphere conifer or the most cold hardy podocarpaceae?

I've got the RHS Dictionary, and that's a mis-cite, it doesn't say it of P. salignus, only of the hardiest podocarps (P. macrophyllus and perhaps P. nubigenus). I'd reckon P. salignus is only hardy to about -15°C, maybe a degree or two lower at best.

Resin

That's not surprising because every other anecdotal reference to Podocarpus salignus that I've found says it prefers a sheltered spot even in a zone 8 climate.

I don't plan on putting any of my podocarps or other southern hemisphere conifers in the ground here, unless they're being composted. I wish I lived somewhere that I could grow these plants as landscape specimens.

So what the heck grows on all these colder mountains/highlands on the South American continent since there were no Larch, Pines, Spruces, Hemlocks, Redwoods to colonize these environments... something always seems to find a way to fill a niche

The simple answer is that the colder mountains in southern South America don't actually get very cold. There is no large area of continental landmass to allow for the major cooling that one gets in the middle of North America or northern Asia. It's an oceanic climate, with not a lot of difference between summer and winter temperatures; places high enough in the mountains to get below -15°C in the winter, don't get warm enough in summer to allow tree growth to occur. The ocean being close by in 3 directions also keeps humidity high, there's none of the desiccating cold-dry winds that you get in the northern continents.

Resin

That's for the most part true, but some of the higher mountains of South Africa see temperatures as cold as -4°F(-20°C) and lowland areas of Southern Chile and Argentina get as cold as -20°F(-28.9°C).(the record low for Argentina is -27°F(-32.8°C) at an altitude of about 900'(274m) and only about 75 miles(121km) from the ocean). Also, there are large areas of the Andes which get as cold as many parts of North America, but they don't get as hot in the summer, like resin said, and they don't have virtually any native woody plants growing. These areas are dominated by grasses and other herbaceous stuff. I also know that some of the mountains of Australia have seen temps as low as about 0°F to +5°F(-17.8°C to -15°C)(the record low being -8°F(22.2°C) in Charlotte Pass at an altitude of about 6,000'(1829m)), but I'm not sure about New Zealand.

I'd think that some Australian, South African, or perhaps some South American(less likely) conifer might be both heat and somewhat cold hardy. Several herbaceous species from these areas are both(mostly from South Africa, rather than Australia though).

Couple things.
Of course, what pineresin says is absolutely correct - however - it's worth noting that the southern hemisphere has a slightly higher adiabatic lapse rate than the northern hemisphere. This is because Antarctica is such a huge reserve of cold, being a giant frozen landmass instead of the Arctic, which is just a cold sea covered by ice. As you go higher the rate of temp. drop is greater than the rate in the NH. So if you could flip the continents but not the poles, south america would become even milder and north america even colder. An esoteric point but one helping to explain why any part of Argentina could reach -27F even though it is separated by over 400 miles of ocean that does not freeze from Antarctica.

Fairweather Gardens was selling an Austrocedrus chilensis found on Cape Cod...not surprising in one respect, because it's an area that has some of the mildest summers on the East Coast:

{{gwi:624800}}

davidrt28,
What data parameter does that map display?

It is this one. Record max for July. My point was simply that Cape Cod does not get very hot compared to most of the east coast (or CONUS for that matter), so the plant has not had to suffer through much extreme heat. Of course Cape Cod is probably still a good bit warmer in summer and colder in winter than where Austrocedrus comes from.

Fairweather has not sold it again since I think the 1998 or 1999 season when they had it, which leads me to wonder whether it was very adaptable.

Here is a link that might be useful: http://www.climatesource.com/us/fact_sheets/fact_tmax_rec_max_daily_us.html

Okay cool, thanks. I knew it was a measure of heat intensity of some sort, just wasn't sure why it was so splotchy.

I know that New Zealand is having problems with wilding pines growing up in their alpine areas, with seemingly no other woody plant competition of comparable height, shading out the nonwoody alpine communities.

Yep, I'd read that too, mainly Pinus contorta.

Resin

The main plants I noticed in the high Andes of Peru was bunch grass. Right up to 4500m, basically just grass and some odd perennials, and a few unknown shrubs.
Below that is "cloud forest" which I didn't notice any conifers in either.