Larger rear sprocket wont widen the use of 1st and 2nd gear,lowers overall gearing.Depends on your style of rideing and type of terrain how low to go,but I would suggest 14-49 or 14-50.Do you ever get WFO in 5th? I like to be able to use all my gearing,so I want to be able to use most of 5th on the longest sraight roads I ride.Lower gearing can make the bike aggressive (just like I like it),just my 2 cents.