Is this good enough for gaming?

Hello.
I just want some feedback on the amount / type of memory i have and how well it'll perform playing games with high graphics (such as Crysis)

Basically.. i have
4 gigs DDR2 ( 2 x 1 GB -rated at 1200MHz Kingston HyperX, 2 x 1 GB -rated at 1066Mhz Kingston HyperX )

Running on http://www.newegg.com/Product/Prod [...] 6813188013

and i'm wondering if it'll be good enough?
Or...should i get more memory? (maybe 8gb of 4x 2GB sticks? or will that be too much?)
Playing games with 4GB isn't that amazing... so i' just wondering if 8GB is twice the performance of 4GB? or is it actually less then twice?

I was also wondering... since i bought this computer build online, I wasn't the one that installed the memories...
And i have no idea how one is 1200MHz and the other is 1006MHz... i'm assuming they're both the same memory cards but... one is over clocked? Doesn't that throw the memory off balance? Because i've been reading some forum posts and they mentioned stuff about different volts isn't a good thing.

In this case, does the 1200MHz have a higher voltage than the 1066MHz? >.>

+1 for using 64bit in order to use 8gb fully.

8 gigs is NOT 2x faster. its about the same speed. Crysis will not use that much, but lots of apps will run better with that extra ram.

If you are against Vista then 8 gigs is not for you. XP 64(any driver/app issues are shared with both anyway) is just not worth it at this point IMO. If you use vista do not be alarmed when windows eats ALL 8(well about 6-7) gigs to pre fetch apps you use often for faster loading.

If you run 1066 and 1200 memory together you either have to overclock the 1066 or under clock the 1200. All sticks use the same speed and voltage. So if you set 2.2 all sticks get 2.2 volts(or as close as the board will get to it)

You set that in the bios. by default it will run with the speed of the slowest memory.

If your gaming performance is suffering with 4gb or ram, then its probably a GPU issue.

Whats your GPU?

Your RAM will not be your bottleneck. Unless you have a very very old CPU, that graphics card will be your bottleneck. It would be much better for you to get a 9800GTX, or better yet, two of them. Their prices have dropped considerably, and your 680i (issues aside), ought to handle them fine, as long as you have a decent PSU to supply them. Crysis is an incredibly graphics intensive game, and you won't be able to put up decent settings with your Quadro.