Currently, my rig has 750W PSU.  With 3 cards running 100%, power draw at the wall is 590W.  The cards I'm using are RX470 4GB, and in GPU-Z the power usage for each card shows as 95-105W while I'm mining.

I'm wondering if I'm able to add another GPU, increasing wattage by ~105W, making my rig run at ~695-700W on a 750W PSU?  Is this trying to put too much load on the PSU?  I know basic mathematics say it's ok, but I don't know enough about PSUs to know if it is reasonable of me to expect my PSU to be under 700W load 24/7.  Thanks for the help!