Tamron AF18-200MM F/3.5-6.3 XR Di II?? I currently own a Tamron 24-135mm lens that I purchased 3 years ago when I got my D100. Although I don't use it as much anymore, it is still my favorite "walking around" lens when I don't want to carry alot of gear. I've been looking at the new 18-200mm for the extra reach. Has anyone tried it? How does it compare to the 24-135mm?