personally I would buy the 320 but IMO its too early to call the 640mb one worthless, at very high resolutions with AF or AA it helps in some of todays games, in games of the future it could possibly help smooth out stutters on games with huge levels or tons of texture detail.
QFT, same way I feel too. I hate how just 1 example of a 320mb GTS vs the 640 in results test makes everyone think vram is useless. This kinda happened with the whole P5N-E 650i vs the 680i. Just cause the 650i barely won 1 SLI test, everyone thought it was light years ahead of the 680i mobo.