Don't worry Ben, it's a good choice.
I would have gone for GT silver like you or black but probably GT silver in the end because a beautiful sport car like that you want it to stand out!
As for being the same color of the future 911 (40th bday) I don't think it's a big problem, firstly bc they won't be many of them and secondly bc it's "only" a 911
Congrats again!
Fanch.
PS: Good choice about the A/C and Radio too! IMHO.