I don't know about the power loss as I've never experienced it myself in anyone else's GTI, I'm iust going off what I've seen on the forum but as I'm looking at getting he Revo intake I'm looking to hear from anyone who has maybe had these same screech noises or moments of power loss like you describe.
As for engine mounts, I will 100% be changing all three and like you say just change the side mounts for OE replacements but change the bottom mount to something more uprated but which one to get, I do not know yet due to the amount there is available and each one seems to differ in how they change the driving feel and noises etc.
Hoping to get some suggestions from people in the know that can suggest the best ones that are best suited to fast road use but something that doesn't bring loads of extra vibrations into the cabin