727 trans cooler fittings

All older torqueflite's take a 1/8" NPT fitting going into them. In the late 80's they switched to a larger fitting. I usually see guys run -6 line but it seems to me that -4 will do just as good. The i.d. of the fitting going in the trans. is 1/8" NPT so no matter how big the line is you put on it'll only flow what that 1/8" pipe fitting lets through. Dash 4 line I.D. is 7/32" which is way bigger than the adapter going into the trans. It would seem to me using -4 line and fittings would do the job just as good if not better since it's o.d. is smaller it might be easier to route and it's quite a bit cheaper.

Hopefully Del "67Dart" will jump in. He knows a lot about line and fittings. Maybe he can verify if what I'm saying is correct, or not