the 15% deal doesnt work like that always. As you go higher in hp the drivetrain sucks up a less % of power.
Just as a ZR1 corvette is rated at what? 640hp or something along those lines and it puts down 604whp or so. That doesnt equate anywhere near 15% drivetrain loss. Your trans is only gonna suck up soo much power. Your drivetrain isnt gonna become more restrictive as your power gets higher is basicly what im saying.
Our cars stock are rated at 140hp at the crank and usually put down between 115-120whp so 20-25hp loss from crank to wheels. You can almost bet this number will stay true unless changes are made to brakes, tires, air pressure in the tires, and soo on. So in reality a motor of ours making 700 crank hp should put down 675-680whp again but most of the time you would be on slicks at a low tire pressure to hold traction on the dyno so thats gonna suck up more power as well.
Anyways back on subject.