you have 2 options.
if you go as low as 60% performance target, you lose a max of 10% performance ( yes, this video card is this good ) .. I believe at a 70% power target you lose only 6%. ( I think its 310 Watts at 60% with not much of a performance lose. but I prefer 70% as its still around 350Watts )
so you can either go that route. and don't worry about the game crashing with you. or undervolt and keep the power target at 100%.
then do a benchmark for any game you have. and see what gives you better performance at the desired temperature.
in my case, for example, my undervolt is 875MV at speed of 2475Mhz. I didn't try to go higher ( even though maybe I should have, but it never crashed on any game for me at this speed so I was like fuck it, it's good enough for me) and to me, the performance is more than what I need and my temp is never higher than 55c for my FE card ( your card should be lower maybe I dunno ).
remember, it's the mV that increases your GPU temp, the higher you go, the higher your temp is and vice versa, that's why 875mV is a good spot for me.