WOW talk about a load of advise my suggestion is to ignore most of it.
I will give you some actual experience comments I hadn't shot my short shotguns in a couple of years but was out Sat afternoon with my Rem 870 12 gauge with my 14" Dlask Arms Corp barrel installed.
Shooting 3" 1 1/8 oz Foster style slugs freehand/unsupported @ 50 yards I was grouping 6" with 2 different 3 shot groups.
I wouldn't hesitate to extent my hunting range to 100 yards with a support and of course after I have shot the distance a bit more.
I had some older 2 3/4" 00 Buck loads that I reloaded years ago with me I was only getting 3 out of 9 .33" balls into the kill zone @ 30 yards.
Max I would use these 00 Buck on deer would be 20 yards.
I'm figuring your choke is similar to mine so you will get close to the same results I do know how too shoot though have had my 2 Rem 870 shotguns for at least 25 years now.
Thanks for the info! Now I'm even more excited to try it out when it gets here. Hopefully I get the same results as you.
FWIW: My Valtro PM5 with 14" cylinder bore, 3" Magnum Winchester rifled slugs, grouping in the 9" pie plate at 100 yards. Haven't tried any different types of slug. Works great hunting water jugs at 50 yds