940be

I've decided HD 6870 or HD 6850 ?? I am using 790GX mobo with Phenom 940BE Proccy My Question is -> Will HD 6870 to use with Phenom 940BE - Will the Processor Bottleneck ?? Shall I Crossfire 2 X HD 6850 with phenom 940BE ?? Will DDR2 RAM is Suffice for Playing Games with HD 6870...