Thinking about buying some Fuel Crank D517 wheels for my truck, a 2003 F350 6.0 crew cab srw. Believe the OEM wheels are 16" and I am debating between 18" and 20" wheels and tires. I use the truck to drive through fields while hunting, tow a boat, haul firewood, etc. Probably going to go with a pretty aggressive mud tire for this and I want to keep the overall diameter the same on the tires so that I do not have to screw around with the speedometer. So, 18" or 20"?

Also, does anybody know the OEM offset so I can get this wheel purchase correct?

Thanks