Either length shell is a fine option for turkey hunting, but I would only bump up to a 3.5-inch load if you're shooting TSS because it will give you more pellets, which creates a denser pattern. For instance, a 3-inch 2¼-ounce No. 9 shotshell has about 814 pellets. A 3.5-inch 2½-ounce No. 9 has 904. That's almost 100 more pellets. And you're already shooting a heavy payload no matter which shot charge you choose, so that bit of extra recoil is worth the tradeoff. For lead, I wouldn't make the same argument because lead means a larger shot size, and an increase in payload isn't going to be as great of a tradeoff. If you go from a load of 2-ounce 5s to a load of 2¼ ounces, that's only an increase of about 40 pellets. To me, that's not worth the extra recoil.