I just noticed that you also drive a Mk6 GTD. So I am in exactly the same position as yourself.
The GTI PP and R were also top of my list. Reviews don't help as a lot of them conclude that the GTI is very good, but the Golf R is simply the better car - and no doubt it is!
However, some of the reviews hint at the GTI being the better daily driver due to less turbo lag, smaller turning circle and less weight resulting in sharper, more responsive steering.
There have also been a few issues with the Golf R. Early models had turbo problems. A few people have had issues with the manual clutch slipping. Also there have been issues with the hadlex clutch pump which mean that people have had a 300hp front wheel drive car
Though hopefully all these issues will have been fully resolved with the Mk7.5
I have decided to buy a GTI PP. One of the main reasons is because I have never had a Golf GTI before. Also, it should be a nice improvement in performance over the Mk6 GTD.
... and the money saved can go towards a Mk8 Golf R.