Just as a side note if you are running windows it won't use more then 4 gigs of your memory. To be able to use all of your memory you need to run 64bit linux with a pae kernel. Even 64 bit versions of windows still use 32 bit word lengths for their memory manager. It will report that it sees all of your memory but it can only address 4 gigs of it.
As the power supply goes get as much as you can afford. That just doesn't mean output but quality as well. I just bought a couple modular designed ones. They are nice to work with. You only need to plug in the output cords that you need. You don't have a bunch of wires and connectors to try and stuff somewhere.
I just bought a couple modular designed ones. ... You only need to plug in the output cords that you need. You don't have a bunch of wires and connectors to try and stuff somewhere.
On the other hand, if you know you are going to use most of the PSU cables, modular is wasted. And if you are on a tight budget, skipping modular will save you some money. Trade offs. Always trade offs.