looking at your kit you running full frame so go with the 50mm to get the ball rolling, hoever, thats one big ole camera to be roaming the streets with, not very inconspicuous, do you have anything a little more reserved?
i run olympus equipment, ad as good as my E3 is, i wouldnt dream of taking it out to shoot street, i use my epl1, far less of a lump and no loud "clack clack" of the shutter just a gentle "click"
but.... my street shooting has evolved to be using flash, off camera and in the day, ala mark choen, bruce gilden to name two so discrete shutter doesnt really come into it.
these were shot with my epl1 (pen) with a 28mm prime (56mm equivilent on 35mm film) with the zone focusing method, as part of a series i am shooting called "grabbed" they have been adapted here for a college project to do with night and day, basically no one person will ever occupy the same spot in the same way twice, just like you can never take the same photo twice.
and as much of a d**k it may make me seem, none of these were shot with permission and there is no exchange afterwards.