Unfortunately, because others have hit a certain speed on their boards with a specific CPU doesn't mean you will hit the same......... I would say you hit either the CPU or MOBO wall, line up ten boards of the same models and all will have small differences where one might need more vcore and others might show more vdroop, variances in the same models are pretty common.
5.3 is quite high and most SB chips don't really get pushed past 5.0 with the volts needed so numbers are skewed but I'd doubt too many get past 5.2GHz. I've gotten mine to boot @ 5.2 but only for boot testing and I needed 1.56v which is out of the realm of usage for my cooling obviously. I would say on a budget board you've already gone far and beyond what most would expect from it, be happy
. But at the same time if that board dies know that it is certainly not the boards fault.... I'm not sure anyone designs $100 boards to run massive OC's in custom water loops, if you can I would say return it and get a better Asus or GB board as they might help your cause or at least an extreme 7 from Asrock.