By my calculations, running at 30% OD on the MPX, it is going to fall on its face at around 4200 rpm and become a huge heat pump and not move anymore air, and thats on a motor that can actually breath.
The rpm you saw the fall off at is to be expected because of the blower inlet plenum and the amount of back pressure the blower itself will be seeing right at the top, which would be in the neighbour hood of around 25psi or more with temperatures of 400+F, simply because the motor itself can't take the air the blower is putting out.
I don't think your car would do very well at the track because of traction issues with that much power down low, and the car falling over on its face because of heat etc.
Nice numbers though .
Haha thanks man. We'll just have to wait and see I guess...