Intel Budget Upgrade (Help!)

Hi Guys, I'm getting to the stage where my system is getting on the old side and I want to be able to play the some of the games that are coming out over the next several months (Black Ops, Crysis 2 .etc). However I don't want to spend too much money on my upgrade. Here are the specs for my current setup

Motherboard - Gigabyte G33M-DS2R
Processor - Core 2 Duo E7200 (2.53ghz)
Ram - 2GB DDR2 (400mhz)
Graphics Card - Gigabyte 9800gtx+
PSU - 620w Corsair

About 4 or 5 days ago I managed to snatch up a second hand 9800gtx+ for $82.50 so what I've been thinking is buying a second 9800gtx+ for around the same price then buying a second hand SLI compatible motherboard to go along with it (ASUS P5N32-E SLI Plus NVIDIA nForce 775 going for $83.00 at the moment on eBay). My first concern with this is that unless I overclock the crap out of my core 2 duo it is going to bottleneck my graphics card setup. Another question I have assuming I do go with this setup is that should I make sure that the second 9800gtx+ I buy is the same brand as the first (Gigabyte) or will I be okay to purchase any brand? I'm also reasonably confident that my Power Supply will be able to run this sli setup but not certain and do you think it is worth buying another 2gb of ddr2 ram? will I get a noticeable difference in gaming? considering its outdated already.

Please let me know what you think I should do. I'd like to spend no more then $300 however I am open to any and all ideas and thoughts!

Future Thanks!