mines takes 1.137 volts to hold a 1 ghz core and 2200 mem oc, which is a good deal more voltage then yours takes... which makes me wonder...
have you stress tested your current oc and gamed for an extended period of time?
my temps never go above 70c but I let my fan ramp up really high at times
personally I wouldn't push it much farther but you could try
that's what warranties are for
I have the same gpu and with the right setup it is definatley capable of going farther but watch your temps