You have plenty of headroom, usually want to follow 80% rule when it comes to electrical components, this includes PSUs that are under 24/7 load. With the 1080ti's, TDP is around 250 depending on model. Taking this, at 4 at 85% TDP is about 850 watts. That is 70% capacity. To hit the 80% rule you would need to hit 960 watts pulled from the PSU. If this is a mining rig, most hardware CPU, RAM, HDD/SSD take another 60-100 watts. So it would put you around 960 watts for 24/7 usage.