Spirit Vs Mp5

So I read this totally awesome thread on the PlusHeal forums about Spirit vs Mp5 for disc priests.

Shame I didn't understand most of it. Threads like that or why I have this blog-I can't be the only one who reads that stuff and gets a glazed over expression. Just tell me what to prioritize, people!

I managed to glean this:
It depends on how much time you actually spend spamming. If you tend to spam, as disc priests are wont to do, mp5 is better. If you do find yourself getting acquainted with the 5sr, then you get more benefit from spirit and might want to weight spirit a little more heavily.
And as I said here, after 1k int, int/spirit gems are more beneficial than int/mp5.

Here is a neat calculator if you want to play with math.

The same thread devolves into a Flash vs Greater Heal discussion, but after a certain amount of numbers my brain melted. I'll touch that topic later. Maybe. If I recover.