I live in CALI and cannot remove it completely.

We have DEQ up north, but it's just some teen agers and you roll up, they plug into your ODB2 and if everything checks out, you're good. I'm willing to bet most of them have no idea what a cat even looks like under there What is the DEQ like in California?

Exhaust backpressure is calibrated into the KJ CRD. When the backpressure after the turbo is lowered with a straight pipe or less restrictive muffler it will cause changes in how the turbo governs boost pressure.

The turbo governing system has an open loop control with a closed loop PID governor working on top of the open loop. Let's say you are cruising at 70mph: The open loop will have the vanes set at a 55% duty cycle, which sets the vanes at about half open. The open loop typically never provides the exact boost pressure the system is requesting so the PIDs go into action and adjust the vanes more closed or more open until the set point boost is reached. With less backpressure the I-part (integral) will load up more than normal and have the vanes more open due to the greater pressure differential before and after turbo. In cruising this is not an issue, but if an accel is necessary it will take more time for the vanes to close and build more boost due to the loaded governors. This may give the feeling of less torque for a bit, but it should recover.

Ideally, if the backpressure is loaded the turbo open loop should be remapped to compensate. In general terms, more open vanes reduce backpressure making the exhaust flow out easier and a slight increase in fuel economy. In reality, tuning the combustion process to be more efficient is a much more effective way of gaining fuel efficiency.