So I was browsing today (as per usual) and came across a comment by Zomgdps which indicated that there may be a veil over my eyes about choices of lvl 90 talents and why we should be using them. To this I sent him a PM to the effect of "What is the math on when I should use the choices and is this really true." Following is a copy/paste of our convo since we figured you all would like the info and it would benefit more people that just myself.

Zomgdps -

Re: Lvl 90 Talent Math

Correct.

The math on RoP and Invocation basically states that unless you can have 93%+ uptime on RoP or 95%+ uptime on Invocation, you'd be better just taking IW and using its passive.

So basically, unless you can ensure you are casting for 56/60 seconds for RoP (or 57/60 seconds for Invocation), you should just take IW and be done with it.

The other calculation is based on whether or not it was worth casting RoP or Invocation in the first place, this is where you get a few extra seconds

Basically, the maximum amount of non-DPS time for RoP is 6 seconds, after which, casting the rune was pointless. Similarly for Invocation, if you cannot cast for 55+ out of the 60 seconds of the buff, it wasn't worth the cast.

But yea, especially if you are busy raid leading, take IW and just be done with it.

Royals - (paraphrase) Uhhhh I kind of believe you but show me a little bit.

Zomgdps -

Its just the IW passive, you don't even have to use it.

The math is really simple, look here:

We know IW passive gives a 1.06 multiplier (6%) passively.

Now take a look at RoP. Say you manage to use RoP for 56 out of its 60 second duration (i.e. miss out on just 4 seconds), the multiplier you get from that is:

[ 56/(60+1.5) ] * 1.15 = 1.0514

Which is a 5.1% increase, hence, less than the 6% passive you will get for IW.

A similar calculation can be done for Invocation, showing that you actually need to use it for 58 out of the 60 seconds in order for it to beat IW passive.

If you start using IW, then things get trickier, but the fact that you can easily fall back on the 6% passive is what makes it such a strong option.

/endcopypaste

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So.. take from this what you will, obviously stacking 15% dmg increase with our cd's will be better than 6% passive if you can be casting/standing in your rune the whole time. But... this is definitely some good food for thought, especially on those fights with some constant raid dmg going on.

Enjoy and thanks to Zomgdps for doing some more math for us while I'm at work!