you can go a little bit more agressive

e.g, 2-3-2-6. Generally speaking, the smaller the numbers are, the faster the CPU accesses the memory, but it also depends on your RAM, speed, DDR/DDR2, etc. There're no definite numbers to adopt. It's the choice between the performance and stability.

The one you were searching for is DRC (DRAM Command Rate). If the BIOS has no place for you to set it, it probably means they dont want you to mess up w/ it ;). Some modules have to use 2T!