This is the choice I was faced with last month, between an 18 month old mk7 GTI PP and 6 month old mk7 GTI. I appreciate that neither was a brand new car so it's not the exact same dilemma but it is similar.
I actually went for the mk7 GTI PP for a number of reasons, I just about prefer the look of the car externally (mainly because I can't stand the mk7.5 wheels) and wanted the bigger brakes & diff. The power being the same didn't enter into my thinking as I always planned to put a tuning box into it and the gains were pretty much the same with both cars. The mk7 was a nicer colour too which always helps, it's in black whereas the mk7.5 was in white and as I don't like white cars I'd have had to get it wrapped which wasn't the end of the world but would've added extra expense. I drove both cars on pretty heavy test drives and felt much more comfortable throwing the mk7 into corners than the mk7.5, just felt it stuck to the road slightly better overall.
On the flip side, I was a bit gutted to miss out of the digital dash as I think it's really smart. However it's nowhere the Audi TT one which is what I'd been expecting before testing it. Equally I do miss the car-play functionality that was in my Polo and is standard on the mk7.5, but don't really want to spend the £200+ to get it added to the mk7. The adaptive cruise control looks nicer on the mk7.5 as well as it's built into the VW badge instead of being in a box underneath it.
All in all, I'd always go for the performance pack option of the two and I think that's more important than getting the mk7.5, well it was to me anyway. So in fairness, if the mk7.5 in their showroom had got the PP then I'm sure I'd be driving around in that car!