some differences between the two:
*55VR refers to 55-300VR, 70VR refers to 70-300VR
1. 55VR is for DX format only, 70VR can do both DX and FX format.
2. one HRI (High Refractive Index) element is used in 55VR, none for 70VR.
3. 55VR is about 200g lighter
4. 55VR has front element rotation, i.e. the filter mount will rotate as it focus, like 18-55, 55-200..etc..
5. filter size - 55VR: 58mm, 70VR: 67mm
6. min. aperture - 55VR: f22-f29, 70R: f32-f40
I think 70-300 is a better choie.