I fly out of Gatwick once a month and get premium security (used to be called fast track) on my Executive card. To answer the first part of your question, it varies. Sometimes I go through straight to the conveyor belt and arch, sometimes there is a queue of 5-10 people and sometimes, belts and arches are closed so there is a longer wait. With the new security lanes at LGW, I think non-premium is quicker than it used to be. I don't think I would pay money to use the service. I would also stress that once you get to the belts and arch, the procedure is exactly the same - it is no quicker.
I'm not sure I understand what Premium Passport control is. When I arrive, I go to the face scan entry machines (as you will be able to if you have a microchip passport) and you're through. I've never waited longer than 30 secs.
Sorry if I haven't understood your question
