This is a bit late really, have already paid for the 4 wheel I have on order but here goes... 
I am having second thoughts about the 4 wheel city mini and wondering if I should have gone for the GT. I have scoured past threads on here, looked at Best Buggy and the comparison tool on the official site but am still pondering. I picked the 4 wheel for stability and because I've never tried a 3 wheel up and down kerbs etc. so wanted to stick to what I know, especially if I use it for a newborn in future. But on other threads people say the GT is very grounded, is if as grounded as the 4 wheel?
Also I've read the GT is a more comfortable push than the 3 wheel city mini with a heavier child. How does the 4 wheel compare?
I prefer the look of the 4 I think and I'm not bothered about the hand brake over the foot brake, but the adjustable handle bar would be good. Fixed handle is fine for me and my partner but my parents will also use and my mum is short, my dad tall so they may like the option. Just don't know if it is worth the extra.