RE: Remy 870
I agree with hunterdeneugene, don't try to hunt with justbeads. This is extremely difficult for even the best shooters. Although smoothbores can be amazingly accurate with Foster slugs, the problem lies in the sights: drill and tap for a scope, which can be expensive, or get a side mount or saddle mount, either of which is nearly sure to mar the finish on the receiver.
You say you think the slug barrel is rifled. Look down it and find out. I've not used the sabots much, mostly because I'm cheap but also because I don't have a lot of 100 yd. shots where I hunt, but my understanding is they don't do much for you with a smoothbore. On the the other hand if it's a rifled bore, I've read that sabots are the best way to go.