Should I switch to 3 finger from 2?

I wouldn't, unless it comes naturally. I do play with 3, but it was just because it was hard not too. But, it rarely gives me an advantage. It just feels comfortable to me. And, I don't use 3 all the time. Definitely less than 50%.

 

Yeah, it depends on your definition of "speed". If speed is playing 16th notes on an open string, then yeah, it will definitely give you an edge up in that department by shedding on 3 finger technique a lot. But for somebody like me who doesn't do that sort of stuff, it hasn't really helped all too much in the "speed" department. I can say, however, that once you get comfortable with it, having the third finger in there adds a lot to your stamina. I can play 16th note funk stuff all day long at 120 bpm, not that that's entirely useful, but it still is a nice thing to be able to do.

 

It can depend on how much time you have to develop the technique. I've tried moving to 3 fingered playing after years of playing with 2. I found that I can play well, but it slows me down a lot. Having to go out and play a gig, I have to revert to playing with two fingers in order to play at speed.

I highly recommend practicing at home with 3 finger technique, though. Even if you don't use it on stage, it can help build up strength in your hand. And maybe being forced to slow down sometimes is no bad thing...