Leave it to you guys to give an answer that may be technically correct but makes the situation WAY more complicated then it has to be.
My advice? Don't worry about it. Since you're still limited by memory speed and have no room for upgrading the type of ram (due to motherboard limitations) I would personally save your money and put it towards a system upgrade sometime this year, unless you can get lucky and find some ram dirt cheap.
4GB to 8GB might show a tiny bit of improvement if you really push your system (video processing, 3d cad design, photoshop, etc) but since you use your computer mainly for Aces High I honestly don't think you'll see any difference. If you did notice a difference it would be due to a clean install of Win 7 more so than the memory upgrade.
There's also the off chance that the motherboard may not even support 8GB of ram, and if the extra 4GB don't match the 4GB you have in it now it can also become problematic.
For a system that's for the most part dedicated to Aces High, I think upgrading to 8GB would be more of a waste of money than anything.