Disc/ShadowFollow

First: Yes, I read the FAQ's. I saw that there are several Disc/Healing builds offered up as examples as well as Shadow builds offered up, but I wanted to ask about possibly doing something different:

Not being a Shadowpriest while leveling.

I would go Shadow until 70 and then switch to Disc, but I want to level with a build I'll do end game with. I was wondering about a 40/0/21 split as seen in that link. I thought my first 21 levels of talents go into Shadow for leveling purposes, then into Disc from there on out. Since I won't ever get Shadowform it would mean I could heal easily, and the deep Disc should help with mana conservation to the nth degree. Is this a viable build for a priest? I want to be able to heal, but going all out Holy I don't think would work all that well because I'd get slaughtered in PVP.

Thoughts?

2 pts in shadow focus will negate the level-based resistance of same-level mobs. 5/5 is for raiders. See http://www.wowwiki.com/Formulas:Spell_hit_chance#How_spell_hit_chance_is_calculated

4/5 Imp Mind Blast fits into your spell rotation perfectly. Mind Flay is a 3 sec channel, Mind Blast will have a 6 second cooldown. the 5th point is not needed.

2/2 imp shadow word: pain is a major damage boost. since you'll likely be healing whenever in a group, reducing aggro from shadow spells won't help you. i'd recommend moving 2 pts from shadow affinity into imp sw:pain

2/2 martyrdom is important for pvp. plus you get crit more often than you would think in solo pve content.

modified build:
http://www.worldofwarcraft.com/info/classes/priest/talents.html?5002323130505120001551000000000000000000000500230410200000000000

Yeah, regardless of the benefits in other areas, SHADOW is the best way to go if you want to level up. Leveling up without a shdow spec will be grueling and relentless. I would highly recommend leveling up a bit then respecting.

If you plan on going PvP, I'd personally change the build to this instead.

You get Improved Vampiric Embrace along with Shadow Weaving and Improved Shadow Word: pain. No need to put all five points in Mind Blast, four is enough, and with +hit on your gear you shouldn't need all five points in Shadow Focus either. Shadow Affinity is for raiding, guess it's your choice, but I'd leave it be and use the points for something else.

As for the Discipline tree, I got you Martyrdom at the cost of 4% cost reduction on instant spells. Martyrdom makes you immune to spell pushbacks after being hit with a crit. I also maxed out Reflective Shield. You lost Enlightment which means your stamina and intellect will take a blow of 5%. If you have 400 stamina, that's 200 health you'll miss out on. Meh.

Anyways, my experience with the Priest class is limited so I might be wrong about it all. Also, the talent build is based on PvP.

The current build on my priest as I'm leveling is enough points in shadow to get mind flay. 5 point in the first rung of holy and the going disc. This should allow my to level fairly easily, it's been cake so far, give me pvp survivabilty and healing/versitility in dungeons. I'm happy with the way things are going but need more 5mans.