I 've owned more than 5 mark IVs / 2 2C+s (which I still have) and all the mark III stripes. My buddy bought a JP some months ago and I've played it several times. In my opinion, it doesn't actually lack the aggression of the early mark series but it does lack the "in your face" and raw tone of these old amps. With the right settings, this amp can be dialed to sound really aggressive. Of course it's more modern and compressed sounding but it has plenty of gain and has all the characteristics the mark family shares. It's super versatile as well. Now, the million dollar question is "Should I get the JP or the Mark IV?" Well, to put it very simply, I would say that both amps sound amazing. Of course it goes without saying that being older, the mark IV might need new caps / tubes ...