Which 870 to SBS?

I have two 870s and was wanting to SBS one of them to a 12.5 barrel. My options are a 870 Express Magnum or 870 Express Super Magnum. I like the option to use 3 1/2 inch shells and would have the barrel cut down and rethreaded for chokes/door breacher. The other (non super) I would buy a new barrel and do the same, CDNN has 870 barrels for $70. What are the pros and cons for both? Paper work is almost done, just need to put the final touch to it for what reciever I'm going to use.

Thanks!

every shoot 3.5" out of a short bbl s/g? The primary purpose of s short bbl s/gun it home defense and more concealable on the road. My choice would be the 870 EM Also the 3.5" shortens your capacity down another round.

I would think the CDNN barrels would be 3 inch at most, so wasted on 3.5 inch receiver SBS.