Re: Similar GeForce cards
As said above, it's impossible to say without looking at the other specs of those particular GPUs - I don't know them off by heart so couldn't say! There's MUCH more to a graphics card than just the amount of memory it has, these days they're essentially little computers in their own right (most cards have BIOSes of their own, memory, processor(s) that in themselves differ greatly, chipsets, etc.
One PC with 2GB of RAM could vary drastically to another with the same amount of memory - you've got all sorts of factors to take into consideration (and not all of these are even on a hardware level!) It's exactly the same story with graphics cards.
Save the whales, feed the hungry, free the mallocs.