8.5 psi here with a 2.6l Kenne Bell. Put down 440 rwhp and 401lb-ft of torque.
I always hear the manual is right at 15% loss where auto is about 18% (whipple and KB sites state that, I don't know for fact).
As long as you don't ping or just plain push more power to the rods than they can handle, it's RPM that will kill your motor. On the dyno this weekend the tech running the dyno asked if I wanted to do a pull to 6800 since power was still climbing steady at 6500.. My limiter is set to 6500 but even so, I would not push an FI setup that hard on a factory short block. Stress on the rods goes up exponentially so you end up with almost double the stress on the rods at 6800 then you have at 6500. I usually shift at 6300 and my shift light goes on at 6150..
Sold: 2006 GT Premium Vert, 5 spd, Tungsten Grey
New toy: 2001 Porshe Boxster S