Wow that's tough.
I'm more of a stock guy, but can appreciate a well done custom.
It really looks great as it is, and yet I love both the GT3 and Gulf looks. If push comes to shove, I'd have to say the GT3 look would compliment that car better. The smaller body of the Boxster can become easily overpowered and cluttered with a wilder, busier paint scheme. The orange accents on the black car will give it punch and menace without being too much.
Just don't drive it through Norman (you know what I mean...
)
Whatever you choose I'm anxious to see the outcome.