None of the Mark IIIs can cop a real C+ tone. Maybe there is one out there that can almost get there, but the 2 I had(purple and red) weren't really even close. Same inherent Mark tone but the clarity, non harsh highs of the C+ and feel are on another level. Most guys that say a III can sound just like a C+, haven't owned or even seen a real C+. I didn't care for either III I owned but I had a SRG C+ in the house. Maybe if I'd never played a C+ I'd have liked the 3 more.
I did play a JP in a store, they also had a IV and I thought the IV sounded better. Not that the JP was bad, it was nice but I was impressed by the IV.