From your write up it seems like you’ve already chosen the SI.
The only thing noted that you didn’t like better than the gti was low end power.
Personally, I would go for a few more test drives in both.
Maybe even go drive a few cars you aren’t really interested in to find out more reasons why you like either the SI or the GTI. Maybe a wrx or a cobalt ss. Maybe even drop down a power class and try out a spec-v or ralliart.
For every one thing you find in any of those cars you don’t like, it should help immensely in your final decision. just my .02
good luck!