GPU GeForce 9800 GTX+
Core clock 740MHz
Stream Processors 128
Memory
Memory Clock 2000MHz
Memory Size 1GB
Memory Interface 256-bit
Memory Type GDDR3

GPU GeForce 9800 GTX+
Core clock 778MHz
Stream Processors 128
Memory
Memory Clock 2246MHz
Memory Size 512MB
Memory Interface 256-bit
Memory Type GDDR3

As you can see, the 512 has alot higher clocks, So if i played say crysis, Would the extra memory help me more than the clocks. Also, could I oc the 1gb to match or beat the clocks of the 512?

It depends on what resolution you'll play. I'll suggest you to take the 1gb video card because with a few clicks you can reach those clocks by overclocking it.

That much difference would make little or no difference in a game, maybe 3 FPS more if your lucky.

Check some benchmarks online for some results on how each of the cards performs.

After testing the two cards in another computer. The 512mb version seems to be much more responsive than the 1gb.
However, I did manage to get the 1gb version clocks to match that of the 512mb and it was stable two.

When it comes down to it, it's how much you want to spend. Hope this helps

Crysis Benchmark:
1GB = VeryHighSpec, OC, 36 - 40 fps

512MB = VeryHighSpec, 34 - 41