If you have already roosted the bird, let the terrain help you choose your spot. You don't want to pre select a fixed yardage only to have a rise directly in front of your position once it gets daylight. A gobbler topping a rise that close will be right on top of you and you probably won't have time to adjust without getting busted.
The closest I'll get is about 75 yards away, cover allowing. Turkeys like to roost together so don't forget that there may be hens and jakes nearby that could bust you if you are just focused on a gobbling bird. Another reason I don't like to get any closer than 75 yards is that turkeys don't always just drop straight down out of the tree. If they are the least bit suspicious or hens have flown down some distance away, they will often glide over your head landing behind you and putting you out of position to get a shot.
One more thing...I'm not big on tree calling either, especially if you are going to try to get within 100 yards. That just helps the gobbler pinpoint your location and he'll expect to see hens on the ground. I like to let things unfold naturally and then call after the birds have flown down.
Have a great spring, Deano!
"The joy of living is his, who has the heart to demand it." Teddy Roosevelt