I have destroyed off road vehicle rims pushing a vehicle over rocks and logs, but have not broken a rim on the road. This is not to say it does not happen - I have seen a cast rim fail in front of me when a truck turned to pull into a parking spot and considered him lucky that it was not at speed. There also pictures posted here of steel rims separating from the vertical center, so don't think that steel gives you more reserve capacity. Method rim models like the 305 NV HD or 701 HD are rated at 4500lbs.
If you need the ability to air down for flotation, These 4k lb rated LT tires with upgraded rims may be for you. If you need a high capacity tire that is more puncture resistant and longer wearing, the move up to 19.5's is worth it and about the same cost.