If you are hitting 53/13 at around 20 mph- your cadence is too low. Well not really as everyone has different styles but you couldl be putting more strain on the knees than is good for them and PAIN can come.

I ride 50 /12 as my highest gear and I rarely use that except on down slopes or downhill. And 30mph in that gear means that I must be going downhill so time to take a rest and concentrate on missing the potholes.