Originally Posted by Jordo!

Synthetic oil is a lot slipperier than dino oil; it's not unheard of to see a gain of ~1-2% in power on the dyno switching to synthetic do to reduced friction.

As to how it feels/sounds as you approach the red, my guess is that after 6.5K the motor is beginning to gradually lose torque, and without different heads/cams or a different VVEL tune, that's just the way it is.