Originally Posted by wildjim
Dig in and take the pain.
I use the 12-25 and 53/39 on my road bike and rarely use the 39t/25T cogs. I mostly use the 53t/21t when climbing and dig in. . .
I am guessing that you are fairly young with good knees. Muscle pain is usually good in training, bone-on-bone type pain is rarely good and should not be ridden through if one wants to ride for years to come.