Back to the 590...
If the matches you shoot at start with fully loaded magazines most of the time, then it would seem that a long mag extension would be of benefit. Personally, I don't like the look of the ultra-long extensions. If you need to poke your muzzle through the holes in a barrier, I would think they'd get in the way.
I also don't run chokes on my 590, and at our matches this hasn't been an issue - even with 7.5 shot. You can always run a couple of matches with a stock 590 to see how it works out and then customize. Although I do admit, "accessorizing" is half the fun of getting ready for a match (at least it is for me).
Either way you go, the 590 or 590A1 is a great choice. I love the location of the safety and not having to push the lifter out of the way when loading is a plus.