Nice work. You have only a few options left now;
1. You can get a modded bios which may or may not let you put in more voltage. But it is a gamble, because a modded bios COULD screw up your board and you will need a new one. It could also not free up your voltage, so it is a huge gamble.
2. You could Volt mod your board, but again that is another gamble. I wouldnt advise that unless you REALLY know what you are doing. Or are simply ballsy.
3. What is your memory voltage? Is that maxed out? You could try a DDR Booster, they apparently work pretty well.
Just my opinion, hope it all works out for you.