"Many people advice 1:1 ratio, but there are also testimonies for the opposite. For example, see So much for 1:1 fsb:dram ratio being the best.
I quote from FSB:DRAM 1:1 ratio question:
The higher clocked the RAM is, the more performance one will get from the RAM. the 1:1 thing is a bunch of bull. Other devices besides the CPU request and store in RAM. Just look at any modern day video card and you will see the RAM clocked 2 or 3X higher than the GPU. Considering the bus of the P4 is quad pumped (4 signals per clock) compared to DDR, which is only at 100, 133, 166, or 200 (double pumped, ie 100 = 200DDR). There is QUITE a bit of lag between the CPU and RAM. So PLEASE stop saying the 1:1 ratio BS around here. The faster the RAM, the faster the access time and the more data can be sent in and out. I am NOT trying to insult anyone here, but I am trying to stop the BS rumor from spreading any further!
Just run Sisoft Sandra at different RAM speeds and see how much more data one can pump through it. Or run any benchmark (3Dmark for example) with the different RAM settings, the higher the RAM clock, the higher the score.