Pattern your gun with a few different turkey loads and decide for yourself. If you have a full choke now, you will probably be fine out to about 25 or 30 yards, maybe more if you find the right load. If you find, as I did, that calling them in close is what makes turkey hunting fun, then you're all set. If having a turkey hang up at 40 or 50 yards before losing interest in you and drifting off is going to drive you crazy...as it did to me when I first started hunting them!...then an aftermarket choke will increase your range 10 or 15 yards, maybe 20. I must say that the most satisfying turkey kills I made were done with old, fixed-full-choke shotguns like my Brno ZP49 SxS.
If you do go through the absolute-maximum-range shooting phase, you might want to try some of the new, non-lead high-density turkey loads. I tried a couple of them and found that not only did they increase my range, sometimes dramatically, but they also performed as well or better with standard full chokes as opposed to X-full turkey chokes. Unfortunately, they were so ultra-expensive that it would probably be just as cheap to get a couple of aftermarket turkey chokes and use lead loads, but they are another alternative to consider.