Oly 14-42 II R or Sigma 19mm for EPL1

I was wondering whether to buy Oly 14-42 II R or Sigma 19mm for my EPL1 that has the original 14-42. I am considering Oly 14-42 II R to get faster focusing (a major drawback with my current camera is the slow focusing). I like Sigma's optical quality and f2.8 but I will be limited to the 19mm focal length. Does it make sense to buy another 14-42? How noticeable will be improvement in focusing speed?