when i taked it to 722 724 it started be inestable on fps on static render (whit gpu capsviewer)
so the limit for me is 720 what is almost half more power than original
but the performance is given in memory oc i taked it to 640 but now i find that is more stable at 638 and 642 i dont use "numeros impares" because it make to freese like 635 637 639
i hope that give you like a help