New system - Advise needed

Hi!

I'm building a new medium system for my brother, and i'm getting some doubts about the right choices on CPU/MB/RAM.
He's a common user that plays a bit sometimes (not a hard gamer) and uses a lot of other applications. He has now a P4 2.4 OC'ed to 2.8GHz and 512MB DDR333 RAM. He uses Windows XP Pro while Vista hasn't a service pack to fix the initial problems.

Here's what i'm thinking now:
CPU E6320 (1.86GHz, 7x mult, FSB1066, 4MB cache)
MB P5B
RAM Kingston Valueram 2GB DDR2-667 Dual Channel CL5
I assume a 10% OC would be possible.

Other Options:
1) Change the CPU to E4400 (2.0GHz, 10x mult, FSB800, 2MB cache) and increase RAM to 4GB.
2) Change the CPU to E2160 (1.8GHz, 9x mult, FSB800, 1MB cache) and increase RAM to 4GB.

Some other questions rise:
1) Do the 4MB cache on E6320 makes much difference over the 2MB on E4400?
2) Do FSB1066 makes much difference over FSB800 when using DDR2-667 dual channel?

Thanks for your answers and advises.