If you need a wide range zoom, IMO, the way to achieve this is to carry a pair of camera bodies with a mid-range zoom on one body and a longer zoom on the second camera.
I have now elevated my kit to a pair of Canon 7D bodies. However I did quite well using a Canon 30D and 40D wearing the 17-55mm f/2.8 IS and 70-200mm f/4L Is lenses. See my China galleries at:
http://rpcrowe.smugmug.com/ all the images in those galleries were shot with the above mentioned 2-camera, 2-lens kit...
The advantage of a two body kit is that I have a focal range of 17-200mm at my finger tips (I do not miss the 55-70mm gap between the two lenses). I have a constant f/2.8 aperture in my mid-range zoom, a constant f/4 aperture in my telephoto zoom, excellent image quality, IS and auto-focus in the entire zoom range.
The disadvantages are:
1. Extra weight, although I can carry the 70-200mm f/4L IS and a second 1.6x body at the same weight as an 70-200mm f/2.8L series lens alone.
2. Extra cost, although a used 40D as a second body is relatively reasonable.
I carry my two cameras + lenses in one of two ways:
1. OPTECH Dual Harness
2. Neck strap for the camera with 17-55mm lens and holster pouch for my longer lens.
There is another great advantage of traveling with a pair of cameras: insurance against missing photo opportunities due to camera failure...