Catman, its good to be able to shoot out to 40 yards just in case the bird hangs up. But it will definitely be to your benefit if you can remain patient enough to let the bird work its way under 30. I think its much better to start out as a new turkey hunter saying your going to try to get him to 20 than saying your going to try to shoot him at 60.
I know lots of folks on here are telling you otherwise, but the first three years of turkey hunting I had I used an old gun that shot to the left just a few inches. If I put the bead where it was just touching the very edge of his neck on the right side, I would center my pattern. I just said to myself, "Put it right on on the right" to remember where to hold. I could have probably killed the birds, by just holding it on them, but i wanted my patterned centered and didnt have the $ to pay for sights.
After getting a new gun a few years later, I learned as REN has said that differnt loads will have a different point of impact as well. I am sure it would be a good idea to shoot at other ranges and more loads if you can, but if not, I still think youve got a gun that will do the job. Good luck to ya.