Congrats on the JSX!
Agree with Nebulous, the ENGL standard cabs sound somehwat scooped compared to the V30 ones. I am not sure that's only due to the speakers though, the construction (wood) is a little bit different as well.
The ENGL pro cabs sound good, i've played the 4x12s at shows a few times and used to own the horizontal 2x12. IMHO, I would say they are worth the price difference to the standard cabs.
Regarding ENGL vs Marshall, it's hard to say - I think both V30 cabs sound really good and really different. Sorry, can't help with that one ;-)