How would I know what RAM is optimal for my...

Enter the MB in a RAM configurator like these and see RAM guaranteed to work in the board. Choose the highest clocking DIMMs from there if that is what you you want. JEDEC standards do not exceed PC26400. So any RAM you use rated above that (say PC28500 1066MHz.) would have to be set up manually to those transfer rates in BIOS.

http://crucial.com/

http://www.corsairmemory.com/configurator/default.aspx

http://kingston.com/

http://conf.ocztechnology.com/index.php?c=1

Those are advertised latencys. For PC26400 try to buy the lowest latency with the lowest voltage required and you will get the best performance available. Latency is adjustable. But if a DIMM is rated at 5 CAS LAT, it may not cooperate if you try to adjust it to run at 4 CAS. So, if you are concerned buy 4 CAS LAT with the least amount of voltage required to run it there. If you plan on serious overclocking, you will have to loosen the timing to 5 CAS in many instances. No problem to loosen timings if you have 4 CAS to begin with.