honestly, and I’m sure some people will disagree with me, but VE is kind of a waste of time, and by waste of time, I mean waste of your GCD time. The mob will already be dead by the time you get damage rolling. You always want to frontload your spells, and wait on the 5 sec mana regen. dot, mindflay, mindblast at +3 shadow weaving. You can always VE a boss if you want to, and most people do. A random trash mob though? mehh, kinda pointless.
Mindflay scales better with spell power. Mindblast, is like double the amount of mana as mindflay. If you’re mindblasting on CD, you will go OOM very quickly. You want to mindblast as few times as possible while maintaining the maximum damage output from it. I only mindblast for 2 conditions: 1, at 3+ stacks on Shadow weaving so that the mana you are spending on it actually does great damage for its use, and 2, to insure that you get the killing blow on a mob to trigger your spirit tap. Mindflay is your main ability after shadow word pain.
So, again, some priests may disagree with me, but this is purely from my experience. When you’re faced with 4+ mobs, to dot all of them will make you go OOM very quickly. As a shadow priest, understand, that when there is 4+ mobs, you will never be top dps. So don’t even try, don’t even bother. Just do single target damage, and let the mage or combat rogue be the star of the show.
That being said, shadow performs extremely well on 3 mobs (I find). You have the mana and ability to dot all 3, while simultaneously mindflaying/mindblasting 1 of them. In a 3-4 mob situation, shadow is fantastic. 5+ though, forget it, save the mana, you don’t get mind sear in classiic.
Very important, as I’m sure you have learned, but you need to spec 5/5 into spirit tap and trying to time your mindblasts (or wand hits) to the killing blow. You have a decent chance of getting spirit tap proc from shadow word pain and mindflay, but your 500+ dmg mind blast is kind of a guarantee if you time it right.
there are talents to limit your threat generation, but not worth it for leveling. What I’d recommend is wait for the tank to establish a couple stacks of Sunder Armor before mindblasting. that should insure that you don’t pull threat.