To address some of WinterSun's post:
1. Many OEM rims are not rated for much over 3500 lbs, so research this before spending money on higher rated tires.
2. A set of four 19.5" tires and rims can be purchased for as low as $2000.
3. The whole idea of going with 19.5" tires to handle weight better. You cannot do this with a soft sidewall tire. If you are looking for a soft unloaded ride or flotation in sand, these are not the tires for you. They will improve load ride and handling.
4. There are aggressive traction treads as well as street treads for 19.5" tires. As with any tire, the more aggressive ones wear faster and make more tread noise than the street tread. I had no issues on forest/logging roads or snow with 19.5's.
5. Although additional tire weight and rim offset has been thrown around numerous times, no one has provided links to substantiate aggressive wear or premature failure due to the use of 19.5's.
6. Suspension spring rate is only part of carrying a load. Proper tires for the job is another part. Then we have shocks, stabilizer bars,...