The gap between 42 and 70 can be quite useful. Recently, at Goodwood Festival of Speed, I found myself having to take off the 70-300mm for the 45-150mm as the former was too close to frame my shots. On the other hand, the longer lens certainly comes into its own in other situations. For lightness and convenience, I think I would stick with the two kit lenses. The zoom offered at 150mm is pretty good anyway for most situations.