Like you, I prefer an honest 275/200 sort of hunting pattern out of my 870 21" 20ga. Thru research I settled on three chokes to experiment with....the Rem SF .572, Sumtoy .570, and Carlsons .575. I shoot TSS...Hals Big20XL load, #9s.
My gun in particular blew the pattern with the Rem SF and was inconsistent. The Carlsons and Sumtoy were neck and neck in performance and I ended up going with the Sumtoy.
Here is a couple patterns for your veiwing pleasure...good luck