Looking to upgrade my RAM

^ Yes populating all 4 DIMMS would make the RAM run slower...
I would suggest you sell those 2x1GB kit and get a 2x2GB kit...Am sure it would work out within your budget...

You didn't mention your operating system?

Definately go for a 4GB kit (2x2GB).

Having all your memory slots filled isn't a bad thing at stock speeds, but I do see you are overclocked a fair amount and I do agree that when overclocking you can run into stability issues using all memory slots available.

Oh sorry, forgot to mention I'm using Windows 7 Ultimate (32-bit).

I'm just confused with the different speeds... like PC6400, PC8000, etc. Not sure how that will affect my overclocking.

Just looked around a few sites and it seems that around $75 won't be enough. Seems that I should be aiming more towards the $100 range... but at that price point should I just go with DDR3 + new mobo & cpu? - a new rig in general I suppose.

Thanks for all the advice so far.  

^ If you want a decent CPU + MOBO + RAM, then you would have to spend far more than $100...

Sorry if I was being unclear but what I meant was if I was going to spend to the upwards of $100, I might as well fork out the rest of the $500-$600 for a new rig. What I mean is I can't justify spending around $100 on something that I won't be using when I put together a new rig.

Anyways... it seems that I was pretty ignorant with memory pricing. I will be looking at $100ish now. In fact I was eyeing this just a few minutes ago: G.Skill 8000CL5D-4GBPQ

Just have to track them down now.

^ Yes...even I understand that...DDR2 memories were very cheap(you could get a 4GB kit for about $50 before few months...) but have shot up suddenly...
And that RAM is a good option...
And I dont see that you would need a new rig for regular usage as the components that you currently have are powerful enough...
And as you will be using a 32-bit OS, dont expect to see full 4GB...For a 32-bit OS, you will get about ~3.5GB usable RAM...

Well I do feel that my current mobo+cpu is holding my gpu back but not significantly where a new rig is in order. I'll probably install the 64-bit version of Wins 7 after I get new ram.

Thanks  

^ That will be good and glad I could help...