I got my mushies up with vdimm mod from x86 (5V line into the vddr). I played with it a bit last night...and umm...4.1V was enough (the mushies dont want to boot at that anymore and freezes if i adjust while already on).
well - this is definately the lowest ive ever seen
http://users.tpg.com.au/weigner/22.jpg
