If you TRULY want a tough, low-sheen paint, check out FPE's paints. I'd suggest the Eurolux Matte or Satin. NOT cheap paint...but once you use it....this stuff falls in the "drool-worthy" category. Their ECO-series Satin would look STUNNING. On a properly prepped surface, it's pretty-much bulletproof. I used Eurolux Matte in my bathroom. It's more like an Eggshell-sheen. Water?!? TOTALLY unaffected by it....any water-streaks look lighter for a few minutes, then vanish without a trace. Faron

Flat, Duration has a slight sheen to it, they call it matte, this is what I would use if affordable.

I used Sherwin Williams Super Paint with a satin sheen the last time I painted the exterior of my house. I was extremely pleased to see the water shed off when it rained. It has held up pretty good with the exception of the West side of my house. Now when it gets wet it appears to soak in instead of shedding off like before. It has become chalky as well. I am about to re-paint that West side. I went online to Consumer Reports.com to see what paints are currently considered the best. There was a short mention of Sherwin Williams paints but none were included in their tests. According to their tests, Valspar and Kelly Moore were the best wearing paints. Valspar is the only one of the two available in my area. On Valspar, they tested Ultra Premium low luster and simi gloss. The Ultra Premium Duramax was tested using flat and low luster. I am wondering if i should use a simi gloss sheen on my hardboard siding on that West side to make it more durable to the effects of that West side sun exposure....any thoughts?

One thing mentioned above is: "will most likely have to be repainted after some years. Wrought iron will rust no matter what (as opposed to an aluminum railing)." is a true statement, there is no paint job wet or powder coat that will last forever. You may want to keep in mind the only way to touch up or repair or simply repaint a powder coat is to uninstall the exterior railing take it back to the powder coater and have them re-do (an oven is needed to bake the finish on) Removing and transporting an existing exterior item is not always easy. If you had your exterior railing wet painted, touchups and re-painting can be done on site. The wet paints will last many years and are as good as powder coat but in my opinion if your item is difficult to move to an oven, preferable.