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That, I couldn't tell you. What I can tell you is, the 6.0 cooler will work towing extremely heavy, in 100 degree temperatures, without worry. If you want to go the Derale route, you can, but it isn't necessary. That fan is one more moving part, that can break.
Better off is a relative term. If you can afford a new one, then there is no worry about any debris from the truck it came from contaminating yours. If you buy a used one, I would make sure it is cleaned well.