I still think the suspension + bolt on route is best. You can add some new wheels and tires too. The RTR wheels look really good on the Mustang. They are a similar style to the Avant Garde and Forgestar F14 wheels some are running on their Zs.
I doubt you'll want a straight-line oriented car out in Germany. There will be too many fun roads and just that fact that you WILL be running the Nurburgring a time or two should be enough to make you upgrade the base suspension and brakes. Mmmmm... Nurburgring...