Shadow Bolt - Required Level 1 - 40 yd range - 5% of base mana - 1.7 sec cast
Sends a shadowy bolt at the enemy, causing 879 Shadow damage.

Drain Life - Required Level 7 - 40 yd range - 2% of base mana - Channeled
Drains the life from the target, causing 104 Shadow damage and restoring 2% of the caster's total health every 1 sec. Lasts 3 sec.

Empowered Channel: Recasting this spell before it finishes boosts the duration by 3 sec. Stacks 5 times.

Character Statistics (at 85):
Base mana: 20553

Shadow bolt cost: 1027.65 (base mana)
Drain Life cost: 411.06 (base mana)
Drain Life cost (5 stacks): 2055.3

Shadow bolt damage: 879 Shadow Damage
Drain Life damage: 104 Shadow Damage
Drain Life damage(5 stacks): 520 Shadow Damage

Shadow bolt damage per 10 seconds (5.88 casts, 5 casts): 4379 Shadow Damage
Drain Life damage per 10 seconds (3.33 casts, 3 casts): 312 Shadow Damage

Shadow bolt damage per 1 minute (35.29 casts, 35 casts): 30765 Shadow Damage
Drain Life damage per 1 minute (20 casts): 2080 Shadow Damage
Drain Life damage per 1 minute (5 stacks, 4 casts): 2080 Shadow Damage (Of course :P)

Drain Life is 28k+ Shadow Damage less per 1 minute of non stop casting, however as Affliction we get a passive ability called Nightfall.

Nightfall (Passive)
Gives your Corruption and Drain Life spells a 4% chance to cause you to enter a Shadow Trance state after damaging the opponent.

Shadow Trance
Your new Malefic Grasp will instantly deal damage and cause all of your periodic spells tick 100% faster for 9 sec.

I'm not clever enough to do the calculations, but I do believe Drain Life will be the 'filler' again due to the Nightfall passive.

What do you think?