Not meaning to brag, but I have taken quite a few toms(well over 25) with 2 and 3/4" 12ga Winchester XXMag 1 and 5/8oz copperplated #5s - my turkey gun is an 870 Wingmaster Magnum 12ga with a 26" VR barrel, with a Remington super full turkey choke, and Firesights on the rib... This load/gun combo patterns well all the way out to 50 yards, and has taken several toms at that distance - but that's about it's limit - at 25 to 35 yards(average turkey shot), it is just plain devastating!!!! My gun also patterns well with Federal 3" #4s - but the 2 and 3/4" Winchester load I described above is my favorite - fairly mild to shoot, and has never failed me... I wouldn't recommend 20ga for turkey hunting, nor do I think that 3 and 1/2" loads are needed, either - after all, the eastern species of turkey I hunt here in NY get about as big as they come, and I've had no troubles taking them with my set-up... Another way of looking at it - for many, MANY years, good 'ol boys were taking turkeys with 2 and 3/4" shells before 3 inchers were popular - so it's not like it can't be done... Lastly, just to let you know I'm not just some wimp who doesn't want to shoot heavier loads - I also hunt deer with an 870 12ga, and ONLY use 3" sabotted slugs in it - so it's not like I have an aversion to shooting 3 inchers - it's just that the 2 and 3/4" Winchester #5s have done SO well for me that I don't see the need to use anything else...
Buy a couple of different turkey loads, and try 'em out with full, extra full, and super full chokes, and pattern 'em at 20, 35, and 50 yards - and go with what provides the best patterns - and you'll be all set... I also wouldn't recommend using shot any smaller than #5s for turkeys - I feel that #6s are too small for such tough birds - use 5s or 4s....
- georgestrings