No problem with using barrel length of 28" or 30" but if you want to be competitive a 20" will get you through. IMO, ideal length is 22", although some SG barrels are longer, they can be cut down to ideal length of 22" but an already available length of 20" in a Stoeger SxS, you're good to go. Although it's a personal preference on barrel length, you need to try out different barrel length and see what you are comfortable with.
I use a Stoeger with 20" barrel that i got used to it and that's what I am comfortable with. Good luck.