Speedy!

I finally got to upgrading my RAM and I've been looking around. First off, I've got a couple of questions...

I'm looking at 2GB of OCZ PC2-4200 ram on eBuyer, for £30 delivered. It's got 4-4-4-12 latency. I also saw some OCZ Pro for £50 which has 3-3-3-12 latency. I was just wondering if there was a noticable difference? Also, the 3-3-3-12 RAM isn't quite right; my PCs RAM is rated at 1.8V, and the OCZ Pro is rated at 1.9V - how hard would that be to change, and would there be anything else involved?

Otherwise, I'm just wondering if there's a massive difference between 2 and 4GB RAM? As in, noticably. I've noticed that lately when I've been running blend/word/corel/outlook at the same time... 1GB just isn't up to it! So it's definately time for an update.