I can remember how my Mark V sounded with KT77 (but at full power and driving EV speakers). To me that was the kick-in the pants fun with the crunch channel. Lower volume settings with EL-34 just did not phase me much, 10W mode was not all that great either and never really made use of it but have on a few occasions. I got tired of the EL-34 type tubes and went back to 6L6 since there is a slight difference in tone and a bit more bottom end. Actually the Mark V was the reason why I began hating the V30 (old cab more than likely the problem).... ear plugs were not enough to get the broken glass out of my ears. It took quite a long time to hate the amp enough to begin liking it again. None-the less, it seems to be sounding much better with the stock 6L6 tubes......Still not fond of the V30 but it is okay with the Mark V, actually my most recent cabs sound great, but I get tired after a while. On the flip side, the JP-2C is amazing though the V30 cabinet of any size. I am blown away how it sounds every time I plug in and power it up. I can play for hours and get lost in the blissful tone at any volume setting. This amp does not come with fatigue built in (this is a good thing), so you need to find that elsewhere or stick with your Mark V if that is your desires. Some love the amp but decided it was not right for them due to difficulty dialing in the amp at lower volume settings. JP-2C can sound great at lower volumes, and very similar to the sweet spot at higher volumes if you use shred at low volume. At first it seems like a one trick pony due to the identical gain channels, it will be that if you desire but it is more than what you perceive it to be. If you have the Mark V, the JP should seem familiar and much easier to dial in a likable tone. Does not have the other voices so it is not as confused as the Mark V. Perhaps it is more bi-polar as it has clean (good) and dirt (evil) channels but they play well together.
If we had a choice for speakers, Mark V definitely needs something different than a V30 (considering the head version of the V). Sealed enclosure EV, open enclosure MC90, Celestion Cream 90W, even a pair of creambacks would suffice. speakers that lack the mid hump on the response curve seem to sound better with the Mark V. At least mine does anyway.
JP-2C definitely a V30 dream amp, Awesome, unbelievable, and many other words I cannot spell or think of... Great with creambacks in a 412, but okay with the EV (sounded flat but you could get used to it after a while).
General tone, it sounds like a Mesa should.... Mark III (yes, with proper settings), Mark IV (yes, with proper settings and selection of power tubes). The JP-2C sounds more like the Mark V- CH3-Extreme but without the ice pick. It would be difficult to replicate the character of the JP-2C using the Mark V with stock tubes. The IIC+ mode does seem to get close but still does not have the mojo. The only way I was able to get extremely close was with a grid slammer on the front end of the Mark V using CH3 extreme. Now that was convincingly close. I have spent more time playing the amp at a lower volume setting since I learned a few tricks to reduce the bass without having to dial it completely out (9:00 basic setting for CH2 and CH3, but depends on presence and gain settings).