Currently the keys available in Settings for the Push to talk key are:
Tab, Left Shift, Left Alt, Left Ctrl, Right Shift, Right Alt and Right Ctrl.
Like, a lot of customers, I am using WASD keyboard to move around with left hand, and my right hand is on the mouse. Occasional use of left shift to speed up movement with my left pinky is fine, but using left ctrl for PTT for any length of time is getting painful.
The main option I would suggest would be the Space Bar (commonly used for “Jump” in FPS games using WASD).