Hi, I got myself a 560 ti and this card is amazing! I saw benchmarks on youtube of people getting 110fps average with max settings (32xAA,16AF,8xSSAA) but when I run mine on the same settings I get only ~40fps and with all turned off I get 60-80fps. My motherboard is pcie x16 1.0 but it can run crysis 2 ultra dx11 ultra textures so I don't think bandwith is really an issue.
Do you have Fancy textures on? I can't remember which it is but in the video settings there's like fast and fancy and I think one other. Haven't played minecraft in awhile. Also your field of view I think will have a issue with frame rates. I could be wrong but I'm only thinking of stuff that I can remember.