When you say you're running CAS3 RAM at CAS2, you don't say what your bus speed is. CAS3 PC133 should fairly easily be able to run CAS2 at 100Mhz. On the other hand, just booting doesn't mean the RAM is stable at that setting. My own RAM (Kingmax PC133) is OK at 3-2-2 at 133 on my BX board in most apps (3 being CAS to RAS), but crashes in demanding ones, like halfway through the 3D2000 graphics benchmark. Actually, it only does this with two sticks, not with one or the other. One of my sticks is stable at 2-2-2 at 133 Mhz, even. At any rate, I've given up 1-2% of system performance to get rock solid stability with 3-3-3. Could be my board is a bit faulty, having trouble handling two sticks, but the potential gain isn't worth the trouble of sorting this all out.
I understand some BIOS just let you select CAS2 vs. CAS3. I assume this is 2-2-2 vs. 3-3-3, but am not sure. My BIOS allows CAS to RAS, Precharge CAS, and RAS to be set independently. (Hope I'm remembering these right.)
I guess it's a matter of how new your system is. When I first got this one a year ago, I tweaked it every which way to boost my benchmark scores. These days, I mostly care that it doesn't crash. And now that I've straightened out a bunch of cr@p in IE and my BIOS, it doesn't.
Now if that Micron RAM gets any cheaper...my head tells me the potential gain from 2-2-2 isn't worth much, but some other part of me wants to brag "my RAM is set to 2-2-2."