Shadow Priest - How much Spirit is too much?

As title says, I wanna know how you manage Spirit on your gear, if you do at all. Right now my itemization is skewed toward Haste, Int and Crit (hit is capped), 2 or 3 of my pieces have Spirit and to figure out how much is too much, I test my mana regen on a 5-6 minute fight, just making sure I never run oom with an expectation of at least 20% mana remaining at the end of a fight. In a raid setting, mana is more abundant but I have limited experience atm. I'm not sure now if I should just give up on Spirit or there's a golden ratio unknown to me.

This is not about rotation, I'm using my mana regen mechanics to their full extent.

It really depends on what sort of buffs are available in the group you are in and how much intellect you have on your gear. If you're in a 5-man, just bring some water with you. If you're in a raid, just get as much spirit as you feel you need to prevent yourself from ooming too often. There isn't any set magic number of spirit, honestly. If your raid group doesn't grant replenishment, then make sure you are providing it for yourself. If you aren't getting a Blessing of Wisdom/Kings or mp5 totems, then you're going to be missing out on a lot of regen. If a fight has adds in it, try and land killing blows on them so that you proc your Spirit Tap.