80% is a nice general rule, and will certainly prevent any power onrush issues, but I think with the numbers you have listed you ought to be fine for the time being. If you want to give yourself some extra overhead power, I'd say just put a Tiptop uZeus or one of the 4ms 4hp power supplies in to power one of the rows. An even smaller option that I've had success with is the endorphines 2hp power. It doesn't sound like you'd need all that much extra power for peace of mind, and any of those options ought to do it.
Cheers friend!