Sure, since I have GT's NP at all.
First Stage- What you already have
Second Stage- 390/750
Third Stage- 395/755
Final Stage- 400/800
Now, if you can get the chip to be stable between 2nd and 3rd (I call this the dead zone since this is where OC lives or dies, then you can theortically bring it up to these speeds: 400/875
That is pretty high, so be careful!!!
Don't push, remember my OCing motto! JUST REMEMBER WHEN DOING ANY OVERCLOCKING, TAKE IT SLOWLY!!
You may have final core clock underclocked a bit like this 385/875, but hopefully your cooling and voltages will be ok to go all the way. GL either way. if you have any questions, PM me ok?