SUV at 6000lbs? That is a very large vehicle. Remember we are talking 7000 "per square inch." Your SUV tire spreads over at least 12 square inches each, technically speaking that you should be able to place an object 12" sqr X 4 = 48" squ X 7000Lbs = 336,000lbs. I don't believe your going to have a problem. The 7000 lbs is measured at the deepest imprint depth to the subsurface. The imprint in your stamped concrete doesn't count when measuring the thickness of the floor because it doesn't offer any support to the structure of the concrete. Basically saying to find strength once the concrete is stamped, you must subtract the depth of the texture to find the actual thickness and strength of the concrete.

All that aside, 5" of concrete should be fine for a non-commercial use driveway. Make sure you get references and take a look at other jobs they have done. It's well worth avoiding a future headache.

Kirk