the apature size is more for using system memory instead of video RAM. Most system memory is going to be slower than video so you don't want to use it for games.
I believe, I say that cause I'm not an expert, that the apature is only used when there are more items to store in video ram than your card can handle. Thus for cards with more ram this won't help...it might hurt if your card decides to offload ram because it's there.
In reading I found that setting too low won't matter as they system kinda takes it anyway.
I do believe that this is kinda like a bios shadow and that setting it does allocate the ram...not sure on this though.
So, if it does help you thats awesome...I, like Batman, didn't notice a difference.