From what I've heard long days with lots of climbing it's not uncommon for knees to feel a little sore. Is that 5-6k feet of real climbing or just elevation change? I can go on a ride along the SoCal coast and do 1400ft of elevation change according to Strava. 70 miles with 5-6k of real climbing is a tough day in the saddle. For most of my climbing I prefer to spin at 90+ rpm which reduces the stress on your knees. Occasionally on 10%+ grades my 34-27 low gear will drop my cadence below 80rpm but that doesn't happen very often around here.