Hey guys. Im looking to upgrade my current lens which is a 55-300 VR lens. I am currently shooting with a D3100 which is fine but i would like to go to a 2.8 lens. has anyone used this lens? Is it sharp? Can it focus quickly? How does it perform generally? another question is what is the difference between the 1st and sec on version? will they bothe focus on my D3100?