I've been playing bass for quite a while, and I use my fingers. With that said, what I am about to tell you may not make much sense, haha.
If you are really concerned with playing fast, I'd say don't be afraid to use a pick. There's no shame in using a pick, and it definitely has some advantages that playing with your fingers doesn't. Speed is one, of course. Obviously it's easier to play faster with a pick. I've noticed also, that I seem to get a nice gritty, dirty tone when I use a pick. When I was in a death metal band, I used a pick to record our album, just because I LOVED the tone. I still used my fingers live, because I honestly feel uncomfortable using a pick.
There's absolutely no shame in a bassist using a pick, and anyone that tells you otherwise is an idiot.