Don't sweat the "native res" issue. It was a worry of mine before I bought my iMac but, now that I'm using it, running games at 1440p really isn't necessary. In fact, it's not always the 'best' way to do it.
By way of illustration; Portal runs on my iMac at 1440p, with most of the detail settings at maximum (no anti-aliasing), at a fairly decent framerate. It's not silky, but it's fine, and I found that it only really showed slowdown when I opened and closed a number of portals in rapid succession in the same field of vision - which I was only doing to make it slow down! I could have played through the game like that, very easily... However, I found that by dropping the res to 1080p, maxing the detail settings and putting the AA up to x4, it achieved a 'better' aesthetic effect. It looked nicer, in my opinion, and it definitely ran faster.
As a general yardstick; I play Crysis and Crysis Warhead at 1080p with all graphical settings on Medium, and they run fine. You get a bit of slowdown when you zoom in and out with the binoculars, but in moment-to-moment combat and exploration, whether in open or confined spaces, the framerate's solid. 1440p? Forget about it.
With regard to the specific games you've listed, I only own one of them. BioShock 2 runs very nicely (more nicely than I'd expected...) at 1080p with all the settings maxed. I imagine that putting it up to 1440p would make it creak - but, in my honest opinion, there's no need.