My brother and I both have one, only took it turkey hunting a couple of times. You can really reach out and touch one with a load of 4's. My first recommendation is to get a sling, the thing weighs a ton and not carry friendly without a sling.
4-6 will work fine. Pattern the gun. I just used the factory full choke and 4's and was confident out to 60 yards. It has been a while but I believe I was using Remington turkey loads.