Removing the u-bend and resonator will decrease back pressure and it might make the engine lose a little bit of low end torque, but it will shift the power band higher and give you the torque where you will need it while racing. If those are the only two things you do, I don't think it will be very noticable.

To counter the back pressure loss from a u-bend and res delete, you could throw a turbo in there

 

I don't really feel much loss of low-end torque and I have a good amount of modifications.