I have two lens and thinking about getting one lens to take the place of them both. I still will keep the two other lens just incase.

The two I have are

Sigma 17-70mm F2.8-4.5 DC Macro
17-70mm F2.8-4.5 DC Macro - Standard Zoom Lenses - SigmaPhoto.com

Tamron SP70-300mm F/4-5.6 Di VC USD
Tamron -70-300mm F/4-5.6(Model A005)

Im thinking about getting
Tamron AF28-300mm F/3.5-6.3 XR Di VC LD Aspherical (IF) MACRO
Tamron AF28-300mm F/3.5-6.3 XR Di VC LD Asph. (IF) Macro Zoom Lens (Nikon) at Hunts Photo & Video - 100 Main Street - Melrose, MA 02176

Is it worth it to get this lens since it can cover a wide range for me? Im using a D300. I was told this lens will work on FX as well.