I let the turkey and terrain dictate how loud I'll call. One of the farm I hunt, I know for a fact the typically roost only about 100 yards away from where I set up, and they almost always hit the field in front of me. In that situation I call very soft just to let them know I'm in the area, then let my decoys do the job. For whatever reason at that farm they are loud as heck while in the roost, then silent once on the ground.

Another farm I've got a lot of wide open fields to cover, so I am normally pretty loud there till I see a reason to change it up.

To put things into perspective though, listen too how soft and quiet clucks and purrs are, yet they get turkeys fired up. They have great hearing, so in some cases loud isn't always better.