Videolaryngoscopy for experienced anesthetists in direct Laryngoscopy

Hello everybody,
We'va got very recently in my department a McGrath series 5 with D shaped blades. None of my collegues have experience with those devices, except me. In fact, I worked  in another hospital,  I've performed more than 20 intubations with a Glidescope titanium. 
My question is: how many intubations an experienced anesthesist in direct laryngoscopy should perform before becoming proficent or at least confident and using videol. when really in trouble?
Could someone give me please also some literature refercences ?
Literature about this topic is really too much and I agree ..."we need quality not quantity"
Thanks