which throttle body

Go with the bbk 78mm, it won't hurt your performance and you should see some gains. The engine will only take in as much air as it can. If the BBK 78 was out 2 years ago I would have gone with it no questions asked.
 
I switched from the Accufab 75mm TB and their plenum to the BBK 78 1 piece. I didn't really notice a difference and I'm supercharged... which means to me their about the same except one setup is 200 bucks cheaper.