That about not lugging the motor...keeping up the revs..important!  I had this demonstrated to me returning up hwy 395 along the east slope of the Sierras through California and Nevada and part of Oregon with a 'weak' headgasket in my inline 4 VW motor..Over some of those passes, I lugged the motor, having recently switched from driving a Ford Turbo diesel pick up..I was used to that, with ooodles of torque at very low rpm and not much up high...Did a few grades in the 2000-2500 rpm range until it dawned on me.  Duh! During those lugging climbs, the combustion gasses really blew into the cooling system, big time!  I had to bleed the system twice in one tank of fuel.  The next few passes, I ran up in 4th and sometimes 3rd, in a 5 speed, keeping it at around 4000 rpm and didn't have any gasses at all when I opened the  bleed screw...
  So on a waterboxer, which some say isn't too strong in the headgasket area, lugging it is probably a bad thing to do..
  Oh, and on those passes, keep an eye out for cyclists and give them room.  Going up a pass like Tioga or Sonora, they are likely to be a bit wobbly. Descending down the other side, they may pass you unexpectedly...nobody checks their mirrors for overtaking bicycles, but it happens on steep tight descents..And at the summit overlooks, if you have any ice cold lemonade, you'll make friends for life by offering it to your two wheeled fellow travelers in the California Alps..
  Don Hanson