Re: Rifled Choke tubes
It depends on the slug. As with rifles, all barrels are at least a bit different.
I have a rifled choke tube for my Rem 870s, and I haven't experienced any improvement or deterioration in accuracy, when comparing to improved cylinder or modified choke tubes.
But I don't have fancy sights either, just the rib and bead. I have all the accuracy I need if I can hit an occasional popper at 50y in matches. Most (rifled) slugs do that.
I recommend you start with your existing choke tubes, and refer to slug manufacturer's recommendations (most of the time cylinder to modified is recommended).
If you want to shoot sabot slugs, I'd go with rifled barrel.