My 2 cents...
Not enough difference in power or response for the BBK to be more money. Both t/bs have been tested in the past by two magazines, Muscle Mustangs & Fast Fords, and Sport Compact magazine. I think SC used the BBK, and MM&FF used the FC. Both resulted in 1-3 horsepower gains across the powerband, and if I remember correctly 1hp peak.
The throttle body by itself is not a big power mod, improves "air flow" and throttle response. Obviously when done with other mods, and in the whole scheme of things, it helps and performance improves with the more you do.
IntakesAndExhaust.com / myFordPerformance.com