Potientially more clockspeed and tighter timings, not all RAM are respondent to higher volts and the higher you go the more chance there is of killing them no matter the cooling. Some RAM is designed and tested to run high volts, like the OCZ VX series and BH5 memory etc.. seemed to like volts without much ill effect but generally i'd not go over 2.8-2.9v with most DDR and 2v-2.1V with DDR2 unless the manufacturer specifically states it. Whats your board and RAM? is it a DFI with the 5v jumper? please note that if you're staying at or under 3.3-3.4v i'd keep the jumper at 3.3 and tweak your psus 3.3v rail if possible because this causes the mosfet to work overtime converting 5v to a lower voltage.