Well I think Priests rule, I will give you some numbers of what I see as I have spec'd and let you decide:
Talents(LVL58):
Shadow:31
Dis:8
Holy:10
All healing still has +10%, my renews +15%
All Shadow damage is increased by 25% (Shadow Form is another +15%)
I usually start out with Mind Blast which does 600+ normally and criticals for 1000+
I then do SW

ain which mine do 192 per 3 seconds and Vampiric Embrace (all instant casts, with a short cool down and I am walking back wards after the mind blast... instant casts can occur while walking)
I then renew myself, heals 202 every 3 seconds for 15 seconds
Or
Mind Flay them until they get to me... mind flay 172 damage per second on top of my SW

ain... which is healing me already even though I do not need it.
What does this buy me?
Perin: hits for 600 ish... he is running at me now (not happy about that)
Perin: SW

ain & Vampiric Embrace(heals everyone in my party) almost on me (both Instant Cast spells)
Perin: Renew(Instant)
OR -- I renew if he is on top of me by then, else mind flay
Perin: Mind Flay 172 each second until they are in melee range. = 516 dam
Perin: Renew(Instant)
Bad guy: Hits for 400 (I wear cloth so I see this at minimum)
Perin: Wand 120 damage (my attack)
Perin: Dagger 40 (cool, it gets in between my wand attacks)
Perin: SW

ain damage 192 (DOT)
Perin: Renew heals for 202 + 40 for VE = only 158 damage total to me
Bad guy: Hits for 400
Perin: SW

ain damage 192(DOT)
Perin: Renew heals for 202 + 40 for VE = only 158 damage total to me
Perin: Mind Blast(1.5 sec) for 600+ (My attack instead of wand)
Perin: Healed for 20% of Mind Blast damage= 120 healed
Bad guy: Hits for 450
Perin: SW

ain damage 192
Perin: Healed for 202 + 40 for VE = only 208 damage total to me
Perin: Mind Flay (My attack instead of wand, channeled) 172 per second, which heals 36 per second = 516 damage with 108 healed.
Summary:
Bad Guy has taken: 2968 damage
Perin taken: 1250 damage
Perin healed: 954 damage healed
Perin has: 296 damage total for this segment as I have around 3400 hp and around 4.5k of mana.
The above was not in shadow form... so only 25% damage increase, Shadow form is cool but you cannot use any healing spells such as renew but your VE is effective still... and your shadow damage is up 40% which actually does a whole lot of damage. This is against a level 60 Skel Lord non-elite... thankfully. Elites change everything and change the way you attack and heal.
For DPS... depends.
I see 250-275 often, I see burst dps of 500+ when nuking but cannot maintain it as the Mind Blast has a cooldown. When I wand dagger them with my Dot... around 150 dps.
I like this because I can heal for my party very well, but also solo when I need to. I rarely go into shadow form, but I am experimenting still with it... when in an instance I am always the healer and I avoid nuking and focus on healing... I use SW

ain, VE and wand... I Mind Flay targets that try to run for it, do not want adds to the battle and look for times to kill fast to get my spirit tap going.
Anyhow, I like this because it is balanced... I can heal and deal a fair bit of damage. A rogue will deal insane amounts of damage, but you better have a good healer
