I am currently using core 2duo e 8400 3 Ghz on XFX 750 I SLI board with 2*2GB DDR 2 Transcend 800 bus ram. I am planing to change it to ASUS P5G41T-M LX 3 and Transcend 2* 4 Gb DDR 3 1333 Mhz . Would it be a good decision to do it & will it increase my performance in gaming?
Core 2 chips are best at a 1:1 ratio with the FSB and RAM speed. So an E8400 has a 9X multiplier x a 333 FSB for 3Ghz stock speed. So at stock the E8400 is best with DDR2 667. If you overclock to say 3.6 then you still have a 9X multiplier x 400 FSB so DDR2 800 is best. I ran an E8400 for a couple of years overclocked to 4Ghz. 9X multiplier x a 450Mhz FSB for a 4.050Ghz clockspeed. I had Corsair DDR2 800 that was overclocked to 900Mhz to match the 450 FSB. DDR is double data rate so effectively that equals a 1:1 FSB/RAM ratio.
A Core2 chip will not see much if any gain from faster RAM. Basically manuacturers started adding DDR3 support to LGA 775 boards because DDR2 is no longer cheap and easy to find. It is certainly not worth spending money on trying to upgrade. Even with the newest Sandy and Ivy Bridge chips you only see a 1% gain going from say DDR3 1600 to DDR3 1866.