My experience has been that, as much as the interchangeable barrels of an 870 or 500 is nice on paper, I don't know anyone who swaps them regularly, and, in addition, a pump gun is a big disadvantage in any of the clay games where you might need more than one shot.
It sounds like you have the defense side covered; go for a benelli with a 26" barrel. You can press it into into defense better than you can press an 18 or 21 inch benelli, or any pump gun, into clay shooting.
Or, although this is outside the scope of the thread, get a reasonable quality o/u for gaming. Horses for courses, and all that.
I have a C. 1940 Ithaca 37; I was lucky enough to find a shortened 21" barrel with a serial number within about 10k of the original at a then-local gun shop (Imbert & Smithers, San Carlos, CA, circa 1999.). The headspacing is done at the breech end for pre-1955 guns. If you can find one that is close, it can often be machined to fit properly.
"If I ever needed to hunt in a tuxedo, then this would be the rifle I'd take." - okie john
"Not being able to govern events, I govern myself." - Michel De Montaigne
"Backstabbers and window-lickers rise to the top of human organizations like oxygen-rich turds in a champagne fountain. I suspect it's been that way since at least the Bronze Age." _ Me. 2016
I've routinely thrown my 28" barrel on my 500 for appropriate activities, and back when I still hunted with modern firearms, often hunted my property with a rifled slug barrel with a cantilever scope mount that I had chopped to 19".
I was into 10mm Auto before it sold out and went mainstream, but these days I'm here for the revolver and epidemiology information.
To continue the derailment: how does one tell how old an Ithaca 37 is?
I bought this because it is nice looking, feels great, is in great shape, is made of steel and walnut and nothing else, and was $200 versus the $800 they want for a new one.
I know little to nothing else about them. I didn't even have any 12g ammo - my only shotgun before this is a 20g Spanish side by side.