I had an overclocked asus 550ti that played single player bf3 with max settings, I usually turned msaa off and only used ssao so that the framerate stayed really but it was playable with it all turned on.
do you have it already? if you are looking at buying a graphics card under 200 bucks i would get a amd 7770 ghz or a amd 7850, or even a 6870 would be better then a 550 ti, the 650ti is supposed to be coming out in the next couple weeks
The lowest end card I'd get on the gtx side of things is a 560 (no ti). A 7850 is the best card for the money if you want to enjoy BF3 at higher levels. I have used a gts 250, a single gtx 560, and 560s in sli in that game. If I were jumping in now, I'd get the 7850 or the 7870.