Both the 600 and 800 are very similar in performance , although the handles are a bit different on each. The 600 series is very sharp and strong with a nice narrow frame. The starmark is nice but i prefer both the 600 and 800.

where are you located?

The 800 is a balanced sweetspot IMO, best performance overall of the 3 and middle price. That said, you really won't go wrong with any of the 3, they are grouped relatively closely. As WoW alluded to, they each have a few options that are exclusive to the line, in addition to the fact that dealers aren't typically able to sell all 3, so that could really make a decision for you if one of those applies... If the 900 isn't out out your budget, you may even consider the 1000 series (HiMark) with 1 3/8" glass and hidden welds if its available to you. That's the real King Kong of the group IMO. The Cellular PVC (900) is a fine option, I'm not sure that its worth a premium though.

Bill, yes, its called the HiMark as I mentioned.

https://www.himarkwindows.com/

The 900 series is indeed the Starmark. The Starmark and HiMark lines have their own "branding" and standalone websites, whereas the 800 on down (envirostar, eco pro, etc) are found on the main Okna site.

Thanks everyone for their comments. We wish to maintain the appearance of our current wood windows, so the 800s in Cherry are a dead ringer for our 'aged' honey oak stained pine windows and oak trim. Seems odd we'd go with a cherry finish however the Melrose Cherry is really a muted color..

A bit disappointed with the trim offered by Okna as it is pine with a matching laminate. I feel we'd be going backwards if we do full tear out and use the Okna trim since we have all oak trim now. We are shying away from the pocket replace since we do not want to lose any glass space, and want the same clean and consistent look on the interior. This is a full restore of both windows and siding, and trim.

I generally refer to it only as Melrose to avoid confusion, as its lighter than most cherries. Very versatile color.

On the install, I like the laminated shoe mouldings when applicable as they kind of wash into the window and don't stand out, however the casing isn't my favorite for the reasons that you've mentioned. I prefer using real wood stained to match. You can still get "prefinished", and even preassembled in a product like Trim n Time: http://www.waudenamillwork.com/pages/TNT.aspx

Lastly, I'd suggest taking a closer look at the install options if glass loss is the only reason that you are considering full tear outs. Often times you don't lose as much as you think, and sometimes none at all, especially if you have storms on the existing windows which encroach on the clear view as well. Your contractor should be able to take some measurements on that to see exactly how that would fall.

I agree, you really dont lose much glass when doing a replacement opposed to a full tear out. Unless its a very small window, i never get complaints regarding glass loss.