What would you do with 5-6k?

If I had an extra 5-6k laying around, it certainly wouldn't be going into a mustang. FFR roadster, trip to europe, house payment, maybe. But definitely not into a mustang. Most of the fun parts I've gotten for my mustang have been cheap fun:

PI cams: new, never used 40$
tweecer which I use occasionally on the 88: $150
PI intake: 20$ from j-yard
Offroad H: $120
underdrive pullies: free