It seems the original poster has been living under a rock.
1. Catalyst has always been problematic on Linux and will stay that way - I switched away from ATI (partly) because I had to wait for a new release of Catalyst (or two) whenever Ubuntu switched to a new X server. And Ubuntu isn't all that cutting edge even.
2. The open-source driver will never be usable for gaming. Ok, maybe when AMD releases Radeon 12770, your 7770 will work better using the open source driver, because AMD would have dropped support from Catalyst 3 years before.
But if you don't care about a usable card and just want to support OSS, then your choices would be ok.
That's right, I'm bad!
2. Depends, but overall true.
I didn't buy the GPU after (forgot about this thread until it hit the front page), and will be grabbing a mid-range NVIDIA card soon to replace the 6450 so I can go back to forgetting that my driver exists. Maybe in a few years I'll give AMD a go again; I won't be bothering after the consistent Fglrx issues I've been having. I still recommend AMD cards for non-gamers, though... the open source driver is great overall for 2d, media playback, and basic 3d.
I'm looking for the best "no-additional-PCIe-adapter-required" card right now and as far as I can tell that's the GT640, but the 640 gets killed by the 7750 which is the same price.
Is there another, better nVidia card that I'm missing, or will it be a case of waiting for the GT640 with GDDR5? (and why is this not already out?)
Hm, right, I discounted dual screens because 1360x1024 monitors aren't sold either. Pretty weird setup you got there, gaming on two different-sized monitors.
 Radeon HD6450 review
 AMD A8-3870K - Radeon HD 6550D Graphics ( Best comparision for integrated graphics )