Well you cant compare them can you, 3" versus 4", a real test is to compare another 3" exhaust with my 3" exhaust, apples with apples and all that. Depends on what power your putting out as well though, you might gain some power/torque low down and lose it top end. We'll see what Jamie's does, definately doesn't hold Steve L's Supra back and that's making well over 600bhp now, probably around 650bhp, may be more.
Steve's is 650bhp easy
Must admit mine feels slower since fitting the whiftbitz exhaust but i reckon half of it is down to the fact is so quiet now and before it used to create so much noise it felt faster. The closed loop boost control has put more duty in though to gain the same boost but with an exhaust that is only 99db its bound to happen. For the price though it really is a awesome exhaust.
Will stick mine on SRR next week hopefully and see whats going on before i put on Jamies old turbo.
Ryan