I would disagree with the above comment. I think its a classic mistake and one which I used to do myself. I used to think that because I had a good core that my body could handle the strain of an extra gear higher when out of the saddle, but unless you're spinning 110 rpm while sitting there is no benefit to shifting up while climbing a steady grade. You will just tire more quickly and be slower in the long run. The key is cadence and rhythm. When doing long climbs i.e. ones that take more 3-4 mins, the most efficient way to go fast is to sit and spin between 75-90 rpm (depending on your pedaling form/power maybe higher) and an out of the saddle effort should only be used for short periods (under a minute for me) if the grade kicks up so as to keep the cadence within that range, or to give the sitting muscle groups a rest. As an earlier poster commented, out of the saddle is slower going uphill than seated so to keep the same speed you need to be spinning faster. Shifting up will just fatigue the legs for no gain.
"Je pédale, donc je suis" - René Descartes (I think
2011 Canyon Aeroad CF
2012 Canyon Ultimate Al