For me the 50mm represents the greatest lens for rangefinder photography in Bangkok. Going longer changes the perspective in a negative way for street which is not portrait photography nor wildlife photography both of which I prefer a long lens and SLR type focusing. In general Bangkok is a very crowded place, my style has developed to where I include the wires and and the nastiness of the city so there is no need to try and isolate them from the framing. I like pictures that I call busy, frames that are pretty full of objects, shadows, people, action, definitions of the moment, interpretations of how I see my world. I see life from two open eyes, not through a long monocular. I try to interact with the subject matter so I want to be closer. The fifty cannot be discounted for these purposes. At the moment I carry two mechanical film bodies, A fifty and thirty five lenses in 2.0 and 1.7, with a hand held light meter so I don't have to point my camera at everything I'm trying to focus on.
One of the complications we deal with on the forum because it is a camera forum is over thinking our gear. Currently it is hotter than hell and double sweaty throughout Thailand, extra gear is a extreme burden in such circumstance. In Cambodia or Laos I would be concerned about having a extra camera body at all times. In Bangkok it is not a worry, If you were to be robbed of everything you could have another camera and lens within a hour and there is always the disposable camera option for dire emergency until you get more gear.
Anyone coming to Bangkok or Thailand try to drop a PM with a phone number, If either me or Simon are around we both enjoy cool drinks and practicing our English, of course Simon's English is much better than mine.