Ive got the 4.5" slash cut K-Tec exhaust with a straight through de-cat and it was worth every penny!
It looks a little odd at first (only cos its different) but its has really grown on me and suits the rear end perfectly.
With the straight through de-cat pipe it sounds like a group A rally car, VERY LOUD!
Also, its made a noticeable difference in performance, peak power gains werent huge (1-2bhp) but midrange was constantly 4-5bhp higher. It also droped peak power from just under the red line to 6650RPM so you dont have to push it so hard. Torque gains were the same, 4-5 midrange & 1-2 at peak. Also peak torque dropped 300RPM too.
Hope this helps
Tom