As a rule of thumb (without getting too technical) you can look at frequency speed and CAS timing. DDR2 800 with CAS 4-4-4-10 will be the same as DDR3 1600 with a CAS of 8-8-8-20. The frequency is doubled, but so is the CAS timings. But where DDR3 starts to pull ahead is the DDR3 1800 and DDR3 2000 because the bandwidth is greater than low CAS DDR2 can make up for...But the most important thing to remember, is that at best this will only give you ~3% speed increase. you'll pick that up in synthetic benchmarks, but not in real world games. And high speed DDR3 is still expensive. better to spend your money on a videocard upgrade.