The JM Pro adds quite a few upgrades to the field model. Aside from the Boron Nitriding of the magazine tube, piston and hammer, the gun has a shorter forearm overhang, a mildly opened up loading port and the larger bolt release from the SPX. The most recent 22" JM Pro we un-boxed also had an enlarged, metal safety from the factory. It also came with 3 chokes, but I believe the last field model I saw had them too.
Also, the following popular aftermarket parts are on the 22" JM Pro from the factory:
Nordic +4 Extension ($75)
Nordic Magazine Clamp ($30)
If any of those parts weren't useful to you, the secondary market would likely take them off your hands and put most of the difference back in your pocket.
William
http://www.OR3GUN.com
Thanks for the info, sounds like a winner! I like the short barrels and they seem hard to find.