The only questions here is I have 667 ram howmuch performance or overclocking difference will I see if I upgrade to any decent pair 800RAM? Will I have to reinstall windows or anything? or do i just put in the ram and chip and go

667mhz PC 5300 = 5.3GB/sec. data transfer rate

800mhz PC6400 = 6.4GB/sec. data transfer rate

RAM speed and timings are adjustable through system BIOS on your MB. Read MB manual under 'BIOS memory adustments/settings'.

You'll see a decent performance gain in synthetic memory benchmarks, but very little in real world scenarios. I have DDR2800 that I run @ 667 because it is at a 1:1 ratio with my FSB. That actually gave me better real world results than running my RAM @ 800, because of the divider that 800 introduced. Unless your adding more RAM in addition to the increased frequency, you'll be disappointed.

As was said above.. synthetics. Straps/etc might actually hamper performance because of latencies in the NB.

Only reason I run DDR2800 is to go 1:1 with my FSB.. only reason it will go over DDR2800 is to run with my FSB... It might run 1066, but that will be for fun to see how the straps work a bit higher.

Agreed... im glad no-one here so far has said something like "yeh do it man youll get 6.4gb/s instead of 5.3 this will increase benchmarks all round faster ram is always better"

Assuming you have a 1333FSB CPU now it would be good to get the 800mhz if you were overclocking thats about the only reason.