Having recently discovered that two 4870 512's don't make 1gb, thanks to your faq, I have a question.
I've just installed GTA 4, in the graphics menu it tells you how much gfx memory you have and how much the options you've selected will use up. At the moment I have it set to use 496/498mb. Now I'm aware that the cards split the load, so I assume 256 goes to each card, but if I were to go over the 498, would each card take more of the load or would they just be overloaded, despite the free memory?
Hmm I've found the same thing recently and I have the same cards.
From what I know now: If you have one GPU with 512MB the game or software uses that memory and if you add second card everything stored to the memory on the first will be copied to the second. This is so cuz when the GPU nees data it can not take it from the memory of other GPUs but it uses its own memory. I assume that if i put 1x1GB card with 1x512MB card they will use only 512MB cuz the second doesn't have free space to put the data from the first... something like that