Funny I have been doing all my (attempts at) Street Photography with a 50mm lens and have been pondering moving up to 85mm or 135mm and seeing how that works. I tend to prefer a fixed lens, somehow the zoom gives me too much fiddle time and whatever shot I thought I saw is gone in the flow of the crowd.
I always aim for 5 foot away (with the 50mm lens) from the individual who catchs my eye and I am often caught due to the proximity. (Aside: My height doesn't help either I fear at 6'6'' but that is another thread about leprecauns are the optimum height for Street Photography)
Anyway, I'm hoping being 10- 14 feet away will make those instances of being caught less frequent.
The main thing is though as I stumble blindly on in this journey is getting a good shot is still such a buzz and long may that continue.