Now, there is obviously a huge difference between the requirements of css and bf3, so if you are solely talking css, you could easily go even cheaper. But for bf3, you will definitely need a little more horsepower (and this should do to hold you over).
As for support, you really can't lump all ati and all nvidia support into 2 separate categories. You have to look at the actual manufacturers. There, some will obviously be better than others. EVGA is obviously one of the most well respected, but I feel that with enough persistence, you should be able to get support from any of these companies given an actual product defect.