There's not a ton of difference but there are better qualities with the 762RC. I think the tone is better with the RC- why I don't know but that's what my Mk2 eardrum picks up. The mounting method is definitely better as it's less susceptible to carbon issues compared with the 762K. Flash suppression is better for sure even without slow motion.
Rangerwalker71 and I went shooting with mine (762K, 762K mini and 762RC - didn't have my 762RC mini at the time) and his 762RC and did a lot of side by side shooting. Both of us were able to tell the difference in "blind" test. Nothing dramatic but noticeable. If you don't have one yet, get the RC for sure, but I still like my K cans too.