Spirit vs. Mana per 5 continued

Well, as I said in the post earlier, I've found that I spend around 60% of my time in the FSR. Ouch. I also determined the formula to see what your spirit to MP5 ratio is.
Spirit = S
X = % time in FSR (as a decimal, so 40% is 0.4)
H is how much spirit it takes to get 1 mana per tick (for priests it's 4)
Q is the amount of spirit continues to regen in the FSR. Priests with Meditation have .15 for example. Paladins would have 0.

The formula is: S = (0.4*H)/(1 - (1 - Q)X).

For a priest with meditation, the numbers are S = (0.4*4)/(1 - (1 -.15)X)

When you plug in my value of X (.6) you get your spirit to mana per 5 ratio. Mine is around 3.25 spirit per mana per 5.

This means that given the choice between 13 Spirit and 4 mana per 5, it wouldn't matter.

HOWEVER

This doesn't account for extra Spirit from talents, like the 5% extra to spirit with Spirit of Redemption, or the 15% extra for tree druids.

This doesn't account for bonuses based on Spirit, like the +10% damage and healing with Imp Prayer of Spirit.

This doesn't account for abilities that regen mana based on spirit like Innervate, Evocate, Aura of the Blue Dragon, and many others.

So use this as a tool, not an algorithm.

However, I did use it to determine that 9 healing and 2 mana per 5 gems are better than the corresponding 9 healing and 4 spirit gems. Also I'll be looking at the 15 spirit to chest vs. the 6 mana per 5 to chest enchant very closely in the future.

Just as a note, Regenfu also tells you in a given fight what your Int to MP5 ratio should be, based on the length of the fight. This calculation is easy. For every 5 seconds a fight goes on, 1 MP5 is worth 1/15th of an Int. So in a fight that lasts 75 seconds, 1 Int is worth 1 mana per 5. Another useful tool, more so for DPS casters than healers.