I concentrate as long as I can, usually up to 2 hours depending on conditions. Then I switch to CC to give my brain and leg a rest for 15min or so.

On flat terrain I use CC set to 60; on hills my foot can control engine load better, and I can coast in N down the backsides.

The key is to GO! Don't stop unless/until you must. One extra stop along the way can turn an incredible tank into a merely very good tank.

Discalimer: Of course, don't take any of this to the extreme and put yourself out of your comfort zone or into danger.