I've got an nVidia GTX 260 and everything runs pretty sweet for me. I'm not saying it'll work in all systems but it's no longer the bleeding edge and can be had for a reasonable cost.
But it's impossible to say "oh get that" because of course, there's so many boards, drivers, revisions, dodgy manufacturers, dodgy builders etc that if BFC was to tell everyone what to buy the customer would be a mite peeved if their system didn't run as others did.
Sorry I can't be of more help.
I guess the main thing is if SF runs OK, the BN will run OK - generally with more trees. Although that's not guaranteed - argh!