I know this is kind of a dated question because GTA IV came out so long ago, but I just recently purchased it so I could use a mod I saw on Kotaku. I have two GTX 460 768 MB cards in SLI, and as you all know, GTA IV requires A LOT of video memory to max out the settings. I still have the limit in place on my game, and with my card showing 730 MB of available memory and 809 being used, high textures and 46 view distance, I can easily get 65 FPS on the benchmark. When I drop to medium textures and max everything else out, I'm not exceeding the memory limit, and I can still get 65 FPS.
I'm wondering how harmful it would be to performance to increase the video memory usage above what my cards have? It's obvious my other hardware, i5-2500k @ 4.6 GHz and 8 GB DDR3 1866, has no problem running the game, I'm just wondering if anyone has any experience running this game on cards with 768 MB video memory.
I've seen people running several hundred MBs above there card's memory capacity using some "no restriction" command when playing GTA IV and they haven't reported an issue. If you are concerned over your video card's condition, I'd recommend not exceeding it's limit.
I have the very same card, (not sli though) and I turned off the restrictions so I can max out everything. It worked fine sometimes and other times the game would fail to load or freeze sometimes. I just tried not to go too far over the recommended limits and everything seems to be fine now. ( I maxed everything but textures which I left on medium) Kind of a bummer since I was able to max out everything at about 40fps with my old gts450, now I get about the same fps you get but can't max everything.
once vram fills up it spills into system memory. this is significantly slower, but may still provide reasonable performance. this game loves system memory too, get lots of it. i used to run it fine in xp with 2gb ram, now i have win7 and it is unplayable with 2gb ram.
if you use settings higher than the amount of potential ram on your gfx, sooner or later the game will crash...
i ran higher settings on my setup due to it having 1 gig of ram . if i stayed in the green. it was fine. if it went in to orange there was a 1 in 10 chance it would crash. if i went into the red then it was guaranteed to crash. you cant physically use more ram than you have. what you see on the display is the potential to use ram.
you will get away with using higher settings than you can handle for a while but sooner or later the game will crumple.