First of all, load ratings by ply count are beyond obsolete. If you're looking to find a higher load tire, stop counting plies and use the modern load rating (two or three digit number after the size and before the letter speed rating). If you choose a tire with a higher load rating, it may not last longer or ride better (may ride worse), but it will haul more weight.
Second, counting plies and comparing construction sales pitches is pointless compared to the design and quality of the tire, and how well it works for your particular application. A tire that lasts forever on a 3000 pound car may have a short life on a 4000 pound car.
I do my tire research by finding tirerack.com reviews for that tire on like-size, like-balance, like-weight vehicles. For example I've noticed some tires that get rave reviews for 4K Lb AWD crossovers aren't as loved by Corolla drivers, and vice versa.