I ran a TruLock .585 ported in my 870 20ga and my Franchi Affinity Turkey 20ga with Apex 9's. Both guns with the .585 threw killer patterns, but honestly were still a little tight for me at 20 yards.
I have since sold both guns, but had I not, I would have hunted a .600 in the Franchi, and was getting ready to try a factory full and factory mod out of the 870. I just happened to sell it before I got the chance. TSS doesn't need to be choked down super tight. .585 to .600 is the sweet spot in my opinion