ah ok...so you're talking about the rated voltages sa imong mems... 1.8-2.2v ang voltages you're mems were tested by Crucial.
you noted man gud slot1+3 @1.8v slot 2+4 @2.2v... mao na naglibog ko

you set the speed & voltages sa mems sa bios. if you set them, then maparehas na na sila voltages & speed.
or if you don't set them, your mobo will set them at default speed & voltages lang.
since these sticks are micron D9GMH, i would suggest you don't go beyond 2.2v for 24/7 use... pwede a little bit above for short benches.
this was my run some time ago... Crucial Ballistix PC-8500 @ 620Mhz x2 (1240Mhz) with 2.15v
http://valid.x86-secret.com/show_oc.php?id=290878