Mario was running those sort of numbers on GTR700 with 3540's with no wastegates I think
Either way its kind of pointless !!!
Full weight car=semi daily driver
Semi daily=turbos that come on sometime in the first minute you put your foot down
I think 1000bhp is about the max a small engine like the RB can manage (even when stroked) before becoming unusable as a roadcar. Ronnie reckons his was about as much as you could actually use and he's about as mental as you can get for whats acceptable and whats not !! lol
Beyond that I think you need to be looking at 4000cc+ for anything useable with turbos big enough to support 1400bhp. You could cheat and use gas but frankly the size system you need for that extra 400bhp will empty the bottles pretty quick and hence again isnt really a practical setup for the road.
J.