I thought it was supposed to be 50-60%. the thing is I I always do incline first so when i get to flat I am shot. but a few months back I tryed flat first and got 335x5, so that was roughly 90% max so my max should be 368 or so and 184 is 50% so 60% is 220. all in all it felt good so what the hell.
A thought on your grip. Load up the bar to say 315-405 and do double overhand grip timed holds for as long as you can. Don't lean back either...make it hard. You need to learn to work through the hand pain for the hercules hold...and know how far you can really push yourself...