Well, I may repent, but I got 3 gig of memory rather than pay for 4 gig, because of that limitation. And it’s pretty spritely, for the moment at least.
It should be. If you did 4 gig, you would get 4 gig - your onboard graphics - any residual loss AND you would probably have Dual Channel speed.
So you would have 4 - 512M for video - about 250 meg of loss.
If you have 3 gig and onboard video, you are losing the amount of onboard video you are using. 3 gig - 512M = 2.5G of memory available.