This is not a specific answer to your question but, here's what I used in China. I consider top-line zoom lenses as a better choice for travel photography than primes because of their versatility.IMAGE LINK: http://rpcrowe.smugmug.com …59682538&k=zS5qP&lb=1&s=A
I traveled and shot for two weeks in China using a pair of cameras (30D and 40D) and the 17-55mm f/2.8 IS and 70-200mm f/4L IS lenses. I also brought a Tokina 12-24mm f/4 but, left that in my hotel safe most days. If I absolutely needed a wider shot than I could obtain with my 17mm; I would shoot a two or three frame hand held pano which is very easily accomplished.
The combination of 17-55mm f/2.8 IS and 70-200mm f/4L IS lenses ON TWO 1.6x CAMERAS is simply the greatest travel and general photography setup I have ever used. See my China galleries at the smugmug.com link below.
The 17-55mm f/4L IS lens, by virtue of its constant f/2.8 aperture and excellent stabilization is a very viable low light glass...
Although the lens is a viable low-light glass, I made good use of a 550EX hotshoe flash. I modified the light with a Joe Demb Flash Diffuser Pro which allowed me to shoot even when there was no ceiling off which to bounce as in this night market... IMAGE LINK: http://rpcrowe.smugmug.com …58911199&k=3wdQp&lb=1&s=A
The 70-200mm f/4L IS lens is light weight. I can carry this lens and the extra 1.6x camera at the same weight as a 70-200mm f/2.8L (series) lens alone. The 70-200mm f/4L IS lens is excellent for capturing images in which the subjects are unaware of the camera and thus are acting naturally... IMAGE LINK: http://rpcrowe.smugmug.com …69470225&k=ehxvk&lb=1&s=A
It can isolate subjects by cropping in the camera... IMAGE LINK: http://rpcrowe.smugmug.com …59064345&k=rZdEm&lb=1&s=A
And it can compress distances making a mundane shot interesting... IMAGE LINK: http://rpcrowe.smugmug.com …59075179&k=jsPrJ&lb=1&s=A
BTW: I would definitely recommend a second camera for any important photographic opportunity. A fellow tour member fell on the uneven sidewalk below the City Walls of Xi'an, China breaking his Nikon DSLR. He did not have a second camera and missed out on photography (including the famous Terra Cotta Warriors) until our tour arrived in Hong Kong where he bought a replacement camera. Additionally, if I had used a single camera with the two lenses mentioned above, I would have missed out on many photo opportunities. This would be even more evident if I had been shooting with primes.