The clicky is a bit more complicated, since you can control it. Worst case is to use it on cooldown, which means +310 Power (+6.3% with my gear) 1/6 of the time, or +1.1% on average for a very long fight. It is hard to see how selective use could more than double its relative benefit, although depending on the length of the fight, the uptime could be more than 1/6 (e.g. in a fight that lasts 2m20s, it is up 28.6% of the time, for a 1.8% overall damage increase; in a 5m fight, it is up 20% of the time, for a 1.3% overall damage increase, etc). Situationally, a large increase in damage for a short period of time may be more valuable than a constant increase, even if the constant increase is larger over the whole fight (which is why clickies have been banished from PvP...)
My memory failed me on this one, I thought the buff was for 20 seconds, but it is 30, which brings it more in line with the other relics:
+6.3% for 1/4 of the time is +1.575% worst case, or +1.89% in a 5 minute fight. By stacking with Inspiration, Zen, etc, it is probably over +2%, quite close to the others.