i picked up an SP10 about a month ago. i've always had a morbid curiosity about the big 10, and one showed up in the gun library at cabelas. i didn't really need one, but it wouldn't let me walk away(being in nearly perfect shape, with beautiful wood doesn't hurt either).
10 gauge ammo is difficult to find here, and when you do find it it's never what you want, and the price is horrendous(30+ bucks a box for steel). i ended up buying a case of federal premium from rogers, at $200 it works out to only about 5 bucks a box more than 3" 12 gauge kents cost locally.
i set up a patterning board and brought the SP10 and my 870 out to pattern some shells. long story short, the 10 gauge patterns as well with BB shot at 50 yards as my 870 does at 30, and with less recoil. if the thing wasn't so damned heavy, i'd shelve the 12 completely and shoot the 10 all the time. 1 1/8oz of #2s at 1560fps(fasteel) was brutal compared to 1 1/2oz of BBs at 1450 out of the 10 gauge. i'd compare it to shooting a heavy target load out of the the 12.
i plan on buying a reloading setup eventually so i can shoot the SP10 more, only issue i can see there is that it throws the empties about 25 feet from where i'm standing, so recovering them might be difficult in some places. i definitely don't regret buying the gun, though.