I was expecting the GTX 460's but not the 1gb. This issue is happening to a lot of other people too - and quite a few of them have GTX 460's 768mb. I was thinking perhaps it might be something to do with not having at least 1GB of vram but that's obviously not what's up with your case.
I still think it's a RAM/VRAM leak. It has all the symptoms. But yeah, if that's what it really is, there isn't much you can do besides waiting for a patch.
Well Thank you very much I think I'll go buy Gta 4 this time for PC