8.25 or 8.75 rear

I've been doing some research and so far, everything I've read says that I'm lucky my factory 7.25" rear-end isn't grenaded in my '65 B'Cuda. As it sits right now, the B'Cuda has the factory 273, but I plan on going either 340 or 360, depending on which I can find a better deal on.

End game, is I eventually want rear disc brakes, and a rear-end that can handle between 350-450HP.

Application is mostly summer driver, with a visit to the strip a couple times over the summer...and if I can find a place locally, likely some autox.

Which rear-end do you guys think is the better investment?

- Dan