What resolution will the games be played at. I don't think there will be "Severe" Bottlenecking. A HD4870-5770 might be the max for that cpu depending on the resolution. Also you could overclock that cpu a bit which would help.
Is there any tool I can use to estimate how a specified machine will perform in certain games? Something where I can define the mobo,proc,gpu,ram,etc, and it gives me an estimation of the fps I would get? Sort of like Can You Run It, but allow me to define the specs of the computer.
Also, if I wanted to run a game like L4D2 or SC2 at 1920x1080 resolution, would I see slow down? According to the latest gpu charts, the gpu I am thinking of purchasing gets about 75fps in left 4 dead 2 at "1920x1200, 8AA, 16AF, Very High Quality, DX9". But, with the slow e1400 cpu, what do you think I will realistically get?
That said, I don't think it is a great idea if all you can reuse is the motherboard.
Even the cheapest G6950 dual core will be much better and not cost more. You can get a 1156 motherboard for $80,
and ddr3 ram is actually cheaper than DDR2 today. Sell the old motherboard if you can and plan on something current.
"The bitterness of the product is remembered long after the sweetness of the price is forgotten"