I spoke with Dustin at Whipple about this a year ago - Was about to pull the trigger and lining up my installation shop when the markets strarted their downturn, so I put the project on hold. Dammit
From what I recall of my conversation Dustin, adding another 150HP per side is easy and the 6.2 should still be reliable. You want more, gonna have to change the exhaust as well. Check the Whipplle Industries website for dyno charts. I thinklow 80s would be your MPH top end, depending on prop and if you change your drive ratio.
You'll need to add oil coolers, but besides that the install looks pretty straightforward.
Running 450+ HP thru the drive is where you'll need to be a little careful - Holeshots and re-entry on a 8000lb boat (7000 dry, add passengers and fuel) could be hard on a standard Bravo 1...