I've been charging at 2C to 3C for at least a couple years, on several packs of different sizes and brands. I track battery IR, occasionally voltage under load and capacity, packs have held up great. Big Caveat, I am fairly diligent with not running packs too low, not letting them sit charged, using a general storage charge range, avoiding heat, using a quality balance charger, avoiding suspect or damaged packs, etc. I believe how they are cared for is at least as important as charge rate for modern good quality lipos.

Which if you hang out in the airplane world, is nothing. Many of the big plane & heli guys, some cars guys too, have been charging at much higher rates for many years. 5C is not uncommon.