Firstly, RAM does not influence download speed
Secondly, that RAM you linked to is unsuitable as it is only 533mhz whereas according to the Gateway specs for your machine it uses DDR2 PC-5300 667mhz RAM. Mismatching RAM speeds is a recipe for instability.
Furthermore, it appears your motherboard will only support 4GB maximum. The highest speed RAM it can take is PC-6400 (800mhz)
If you can cancel any orders, I would. Your best best option would be to find 4x1 GB sticks of 800mhz Ram. Gateway Support - 1015002R*Gateway GT5656 Desktop Computer Gateway Support - Components list for 1015002R
At any rate, 7GB would not help you performance wise. It would likely hinder it.
The biggest frame rate killer in Crysis are the shaders. Also make sure you have Anti-aliasing off. I'd also lower that resolution as well. Keep trying a combination of MED/low to find an acceptable level.
Sorry for the bad news mate, but that rig will struggle to play Crysis smoothly with any decent graphical levels