The opinion of members will be appreciated.

I mainly do avian photography.

Is the use of a 500(or 600) F4 lens without a 1.4 TC favored above the lens with a TC?
I know that you lose 1 stop with the TC but I normally shoot at 5.6 or more in any case for DOF.
Secondary effects such a small loss of sharpness and speed of focus may also be a problem.
Also you will probably crop more without the TC.

Thank you.