Why would they release a 560 faster than a 6970, that would render the 570 useless lol
Its a rhetorical question which is already played out with o/c 6870's that bench similar to a 6950/ even 70 in some cases.
But the 2 series have different architectures, so the results/behavior are different game to game.
Same applies to g110 and g114. different gpu's. That don't behave exactly the same. The gtx 570 has a 320mb interface its memory is clocked at 900mhz (vs 1000 on the 580) and its core is 730, the gtx 560 will indeed be nearly as fast (especially factory o/c) in some games with its 384 cores @823mhz, imho.
What else separates g110 ,g114 ? the ability for 3-4 way sli, faster, larger memory sub-system. 1.2gb, 40-rpo's etc .
Imo, Nvidia also benefits from
extra performance in tessellation heavy games and
yes the dreaded physX titles.