"which would you get and why?"

Without a blink, the D7000. You are well equipped in the lens department. Yes, the D7000 will produce better images than the D5000, but also consider just some of the shooting and handling features of the D7000:

Pentaprism 100% viewfinder; -Superior autofocus; -meter functions with manual focus lenses; U1,U2 modes; external controls for fast operation; dual card slots; read the Nikon USA tech specs for more. For your action photography, the D7000 will take your photography to another level. Shooting on CH (Continuous High), will fill the buffer quickly, so your strategy may include burst shooting, and shooting large Jpegs for action.

With my D7000, I use the Tamron 17-50mm f2.8 that I purchased with my D80. The main advantages that the Nikon 17-55mm f2.8 holds over the Tamron are superior build quality, and superior autofocus -- a definite advantage in low-light shooting environments.

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