I may regret it if I don't
That line says it all for me mate.
I've been and done the whole 4+ (probably like 7) years of driving a petrol car I absolutely loved and so glad I plucked up the courage to get the one I truly wanted and enjoyed every minute of it. When the time eventually come to change I thought, ok time to be somewhat sensible now. I looked a really nice car I wanted, then looked at its diesel equivalent.
For me swapping to a diesel equivalent of a car I really wanted was a mistake (absolutely nothing wrong with diesels though!) It just wasn't... "me".. I looked at the tax, the running costs, the insurance etc and all that pointed the diesel to be the more logical decision, however for me that enjoyment just isn't there for me.
I've done the "should I, shouldn't I" twice now.. First time I stumped up that little extra and got the petrol one I really wanted. The second time having had that enjoyment I thought I'd got it out my system and went for the diesel version and I personally wish I hadn't. I'm not sure it ever goes out of your system
Even though its bugged me ever since and I've regretted it (again, nothing wrong with the diesel) that feeling of... regret has never gone away for me. The Plus for me now, is that its led me to this new GTI and so the decision for that over the GTD was easy for me, although both great cars.
What I considered to be the key points / bonus' for me with the new Mk 7 GTI is that...
The tax is like £125 UK now? That is lower than most other cars I like, most of those are £180+ and others much higher, high £250 / low 300 I think with recent changes? Yes its not as low as a diesel, but would you swap the difference for the enjoyment / feeling you get of getting the car you really want?
Insurance different for me between GTD and GTI is like £20
GTI has higher running costs yes, but again its still better than many other cars I would look at. I will also get that enjoyment I don't feel I'd get if I didn't go for the model I truly wanted (regardless of engine). I personally don't mind the extra trip or so to the pumps for feeling I get and the sound of the exhaust alone
Obviously your decision to make, not sure if this input helps. A big longer wait might be a bit of a pig, but it would be worth it. However I've only been waiting 5 weeks so far and each day feels like a week, its painful lol
I'd say don't live with regret, some things happen for a reason, maybe your trip to the dealer was just meant to happen?
Good luck with whatever you decide