Find you a .585 trulock, .572 remington super full, and an Indian Creek .562.
All three are known to shoot tss well and the other two will be easy to sell in the classifieds come spring.
My gun (870 21" barrel) preferred the remington super full .572, but I would have shot the trulock as well. Trulock was a very even pattern. My 870 did not like the Indian creek at all, but iv seen some awesome patterns thrown with one from other barrels. Just have to see what your gun likes. I tried a 18.5", 21", and a 26" barrel on my 870 and all shot different. I settled on a 21" barrel, remington super full, shooting 2oz of tss 9's.