I feel like I answered this one before.. but Mech_engineer's answer closely mimicked my answer..

If you guys intend to modify your cars, you really need to understand the ramifications of your modifications.. Spiking and Creep are two different things, and an MBC doesn't have much of an effect on either..

Spiking has to do with the boost overshooting your setting, typically its caused by the vacuum source your using to operate the actuator or the volume of boost/vacuum and length of the lines your running.. all can affect how quickly the actuator can open and will influence if you have spiking, and how much..

Boost creep is basically exceeding the flow of the wastegate.. the stock Evo turbo flows more than enough gas through its wastegate to not really have issues with boost creep, unless you increase the airflow through the engine significantly such as a stroker kit or a larger compressor and wheel in the turbo then porting of the wastegate will be necessary.

There are two things that you should always check though.. There should be adequate preload on the actuator not too loose or you'll have trouble with boost, and not too tight or the wastegate may open late and actually cause a little boost spiking.

Generally boost controllers are more prone to spiking because of how they work, their restrictors of flow, and therefore may take longer for the actuator to get the signal to "Open" the wastegate... Like I said earlier, length of lines, type of boost controller, diameter of the lines, and the source for your boost/vacuum will all have an impact on your boost curve (Spool is generally not affected)

I think this is a fairly accurate bit of info.. forgive any minor errors since I'm typing half asleep..

 

thanks Jack for answering on PM and this thread