I've recently been experiencing similar problems in Rome Total Realism VII. But it's random and not nearly as bad as your problem. Plus I just reloaded my bootcamp partition and think I might be missing an Intel driver update.
I would suspect VRAM right off the bat, at least it's usually related to it in the past 18 years or so of experience I have. It used to be pre-AGP you could actually swap out the memory on the card. Secondary to bad memory, I would guess a driver.
But as I understand it, there is no VRAM. It just uses some of the base memory as VRAM. 384MB with 4GB or less, if you upgrade to 8GB it will use 512MB as VRAM. So it might be related to this new memory. Addressing it wrong, at the incorrect speed, who knows...
The first thing I would do is swap your old memory back in and see if it still happens. If it doesn't put the new memory back in. If it still occurs after putting the 8GB back in, start looking into brand, speed of the new memory, etc.
Personally I think that there are probably some driver tweaks that can be done by Intel/Apple to improve the reliability and efficiency of this chipset. I've been pretty impressed with what it can do for what it is. Here is to hoping they continue to update the drivers.