Hello again Mike!
Not sure if this will help, but I had the 5770 before the one in my sig, which ran the game ok on medium settings away from London at 1920x1080, but that was before all the recent improvements to the game. At your lower res, you could probably fly on medium over London too with the 7770, or possibly tweak things higher.
Whichever card you pick, make sure you turn off ssao and AA in the game and let CCC or NCP add CSAA (FSAA??FXAA?? Can't remember). A search on the forum should bring up recent tweaks for ATI cards.
I'm really happy with the GTX570 though, which I bought a year ago. No intention of upgrading this year, works fine with everything on high, original textures, effects medium. If you could run to one of these I think you'd be happier than a 7770. My opinion, you understand
