Well I get tired easily, probably around an average or thereabouts, but the reason is that I deliberately go fast on solves to reach the best times I can. When I just barrel through and do 50+ solves in a row I can definitely complete the solves but my times are 1-2 seconds worse, and it's really worth the break every few solves to shave that time off. For example when I did the real man's average I got an average time of 29 seconds, much worse than I usually do (because I take breaks). But there was no problem actually completing the solves...