I've been the happy owner of a Nikkor 18-200mm 3.5-5.6 VR lens for a couple of years now. The range is amazing, the VR is of much help in low-light situations, and I don't need to change lenses and clean the sensor every other week. Problem is, I want a lens that's sharper and faster... with the convenience/advantages of the 18-200 listed above. What alternatives do I have? Budget would be $1,000 (part of which would come from the sale of the 18-200). Thanks for the help.