Those temps are good (using coretemp right?) You can undervolt memory just fine so long as it's stable. My DIMMs are rated for 2.2 V but I run them lower also.Temps are around 25-30c idle and 48c load. I ran Orthos for 30 mins I don't have enough time to try for any longer, but I think it's fine. I also played Crysis for multiple hours no problem.
One more thing, my memory voltage is at 1.79v as reported by speedfan when it's rated for 2.1v, is this okay? I can't really type in an exact voltage in my BIOS it only has DDR2 OverVoltage option to give + amounts of volts.