Which rear 8.25 or 8.75 swap for new project

As long as your not beating the crap out of the 8-1/4, it will last with over 400hp. If equipped with slicks and the car is heavy, you can expect a shortened life.

If you have street tires and cruise the Blvd. you should be just fine. You can save a lot of money if you wait on the installation. At the price offer d for the 8-3/4, I would certainly pick it up.