I've tried the classic Affliction+Improved Void Walker and just tried Full Demonology, Demo is much better. 9/31/11
https://classicdb.ch/?talent#Ii0bZbghzTxotZVx0z
Basically I put all points into demo until SL (Soul Link). You will face little mana/resistance issues up to 40 and casting Corruption/Immo/CoW or CoA then SB+Wand gives enough time for VW to do his thing. VW accounts for about a third of my damage.
Shadowburn is amazing, I can not stress this enough, dramatically improves kill time.
I really like Gnomes on Ally side and Orcs Horde side.
At 60 I recommend 3/3 Improved Succubus for when CC needed, otherwise Demonic Sacrifice it and you will be pulling 150-180 DPS over 5 man runs with questing gear. (Don't start SB spam until you see x2 sunder or aggro will be pulled). VW Sac+Hellfire for serious AE if you feel brave.
Mages obviously nova mob pulls we tank mob pulls!