Verneq, I'm assuming you're referring to the Ronnie McCoury J75's (at least that's what my package says). I put a set of these on my Breedlove A & like them real well. They have good tone, are plenty loud & don't bother my fingers any more than J74's. They don't seem to be affecting my mandolin at all & they seem to really last. I've had these on for about six months & are still sounding good (not dead at all, although my guitar does get more playing time). I wouldn't consider these heavy, but slightly thicker than mediums. As far as speed goes, I can't see how these would slow you down any. My speed problems aren't the fault of the strings, but rather my playing ability. All instruments are different, so about all you can do is try them for yourself. Good Luck & God Bless.............J.W.