^ok that will do great.
i believe you will see a performance difference while gaming by upgrading your CPU.
it will not be "cost effective" to upgrade that motherboard and get another clostly 560ti448 to SLI while you have a PIIx2
a motherboard i suggested PCI Express 2 (x16, x8) <--- what you need to SLI
and add in a PIIx4 955 because really a dual core just won't make it; so before you even get another 560ti448 that is going to cost $190. the cheapest 560ti448 i found was:GIGABYTE GV-N560448-13I GeForce GTX 560 Ti - 448 Cores $269.99
$249.99 after mail-in rebate card
for a total of $440
now you may forgo the CPU now and see how bad the system bottlenecks with picking up the mobo and 560ti448. which will make it $340.