As far as deleting the u-bend i can personally attest to this increasing the power somewhat being as how i recently had this done and had the resonator deleted. I noticed it as soon as I hit the gas to pull out of the exhaust shop parking lot. Thanks to the resonator being removed the exhaust is also noticeably louder as well. Now as far as the Cat. Converter goes it might be getting plugged up i would go to a reputable exhaust shop where you live and have them check it. If it plugs up completely it will leave you on the side of the road.
Hope this helps.
