Actually the 6870 gets pretty good framerates in Crysis at 1680x1050 thanks to driver optimizations. Make sure you have the latest patch for Crysis.
As for your CPU yeah a Phenom 9850 may be a little low end for that 6870. If you can overclock it to at least 3.0Ghz that would certainly help.
Yeah, but to be honest, even with ACC that can be pretty hard.