I've think the best strategy with great performers like PBA is never to sell your entire holding. I learned that lesson with ALA.TO. A more balanced approach, if you think there could be a pull back coming, is to sell only part of your holdings. This way you can lock in profits and possibly buy back shares later on at a lower valuation.
At this point I am not selling any PBA.... maybe if it hits 40 next month I'll reconsider : )