There is no option to change RAM Command Rate in the ASUS P5KPL AM/PS bios. I use two KVR DDR2 800 2GB 6-6-6-15 in Dual Channel Symmetric mode, so 4GB total. CPU-Z shows that my command rate is 2T, but I want to change it to 1T, because 1T gives better performance over 2T.
1T/2T--it only makes a slight difference that you will mostly only notice in benchmarks. It's worth setting if your RAM will run it, but it's not worth adjusting your primary latencies over. You might just be able to run the other timings tighter instead.