Ok this will sound like herasey but: the one and only time I EVER came hands free, was not by some massive cock (and I have had my share) but by a guy who was between 4 and 4 1/2 inches. He had a wicked upward curve, and a crow-bar-to-pull-his-cock-away-from-his-body angle, and with my legs over his shoulders, he could get me there almost each time. Something about his penis shape, head shape, and they way it would hit rapidly across my prostate, hitting on the in stroke, flicking and scraping across on the out stroke, made me shoot damn near every time.
A longer or thicker dick, for me at least, while giving wonderous feelings, has yet to accomplish what his modest endowment did.
Point being: every bottom and every top are different, and using blanket statements like "you just need blah and you will be assured blank" is a dangerous practise. The smaller guy worked for me. My larger current guy has come close (curves left) and may do it one day. And if they he does? Woo hoo! It will mean that I am not denied that pleasure just becuase the equipment is different :biggrin: