The 5870 offers better performance currently, than the 6870, but uses more power and is not as scalable in crossfire as the 6870. The GTX460 is 1 tier below the 6870, not that much. Anything within 3 tiers would probably not be a noticeable difference.
Thank you for your reply...i snagged the 6870 Black Edition and i'll plan on CF'ing them in the future.
Furthermore - since the 6800 series is here, i'll have trouble getting warranty in case of manufacturer defect with the 5870 - i had the similar issue with the 4850 512MB card - good card when it came to gaming, but it gave me BSOD's (nearly a year back thas why i swapped it added a lil cash and got the 5770 for Rig:2)