I won't be of much help relative to the IR-J, but I've owned and gigged the actual JEL25 head, owned the IR-X, and currently own and have gigged the IR-D.   The JEL25 head was underwhelming, didn't do it for me but to be fair it was in a fight with my Wizard MC25 and really was just there as a backup just in case.  When that just in case moment arrived it was painfully obvious what was a better amp (at least to me).
The IR-X into a Fryette Powerstaion was a monster but after I added the Powerstation it was just as dumb to cart around that much gear so back to a backup head I went.
The IR-D was a recent thing that I run into a Seymour Duncan Powerstage 200 and out to a regular cabinet.  So far that has been outstanding, kind of a mind fuck actually.  I've used it on two different gigs in the last month when I couldn't have my regular rig there and it has performed perfectly.
So if I take my JEL25 experience and compare it to my IR-D experience, the IR-D will win hands down.   The IR-J apparently has a built in tube screamer circuit (could be wrong about that) but based on the two actual channels on the IR-D and how you can set it up, I think the IR-D might be the most versatile of all of the IR series, especially since you can hit it with a pedal.   The IR-D with a clean boost up front is a monster.  You can also find the IR-D much cheaper on the used market than the IR-J.
I wouldn't buy the IR-X again, I would probably check out a full 50 watt JEL head, but at least for me the IR-D is the winner out of all those choices.
Check this very good comparison: