I would think the 500hp RB would take more fuel because of the forced induction, it's more dangerous to run lean in a forced induction engine then a naturally aspirated engine, so usually when a turbo car is tuned, it'll be a little on the rich side to make sure it never goes lean. Even tho, a 500hp LS1 will most likely have a supercharger....I dunno, but there wouldn't be a big difference, I'm sure.