Every rig has it’s sweet spot, you just have to find it. As Yerr0r pointed out - one of my rigs with two gtx 1080ti’s runs great at 80% power, +200 gpu core clock and +550 memory clock, fans at 70%. I built another 4 card rig, same motherboard, processor and GPU’s (MSI gtx 1080ti Duke) and it’s unstable at anything more than 80% power, +175 gpu core clock and +300 memory clock. Start with everything at 0, see if it’s stable then go up in increments of 50 until it gets unstable then drop back some and see if it smooths out. Realistically if you want good temps and low electricity usage then you should look for the area around 750 sol/s
Good luck!