For most situations if you're putting the SUV up on 4 stands @JPhi1618 is correct, only 1/3 to 1/4 of the vehicles weight is sitting on each stand. I have put a Toyota Sequoia on 3 ton stands and they are steady as a rock. The Sequoia has a curb weight of up to 6,000 pounds. At that I was still no where near the rating for each stand. Even putting just the front or rear on stands (with both wheels on the other end tightly chocked) the end on the tires is still holding roughly half the weight of the SUV.
Two 3 ton stands holding up the front end of a 6000 pound curb weight SUV will more than do the job since each is only holding at most 2000 pounds. (front end is heavier, so call it 4000 pounds front, 2000 rear, and there are two in the front, so 2000 pounds each).
In the end, buy the biggest, best, highest rated jack stands you can possibly afford and then treat them like gold. Don't let them get rusty, etc. Literally your life depends on them doing their job.
One thing to be careful about is the height to which the jack stand will rise. The Sequoia has a very high ground clearance so the jack points are also high off the ground. Be sure you get jack stands that are stable when extended high enough to give you room to work. That might be harder to find. I have often used ramps backed up by jack stands (drive up on the ramps, put the stands in place but not 100% extended in case the ramps failed) to give enough room. Just make sure the ramps will handle 3 tons as well.
Also be sure of the jack stands footing. The wrong kind of stand might sink into your driveway on a hot summer day.
Hope that helps!