I don't think there really is that much loss on the bottom. A good friend of mine has s4s and he still has a strong bottom, but it really picks up at 5k compared to stock. note this is NA. I am guessing the bigger cams would need more work with timing...
Wouldn't a GT40R be a little..........er................much?
The only concerns i have with going TOO big turbowise, is tractability and gearbox longevity. Seriously considering getting the gears cryo treated and shot peened. I have head of people welding the gear box housing in certain areas where it will flex under the excess torque. But i have no idea where to get the welding done.
yes it holds more than all of our other weaksauce gearboxes, but it doesnt mean that it will handle a setup that will be putting down over 500 whp easy like a C3+ GT35R and up would easily produce. Like i said before. Sell the parts and go with S4's. The best cam made period for a car that will be driven on the street for any setup.