If I understand your question, the response time for course corrections is about the same. The AP will drift off course due to wind and current but will make a correction based on the compass heading set. The IP is based on GPS, but you have to be using the recorded track feature (playback) to get the gps accuracy over compass heading. If you are actually doing the recording, I would imagine that the AP is doing the driving while in "record" mode with it collecting the gps data as your move along, then in playback mode it uses gps data to keep you on the same course you just recorded. If you or the wind pushes the boat 25' to one side while recording, the playback will follow that 25' variance as well since it was recorded via the IP. There is still a bit of slop in the gps data as noted in the various comments on the spot lock feature in IP. GPS is accurate, but only down to 10-20' +/-.
GO BIG ORANGE !
I meant to behave, but there were just way too many other options available at the time.