Chain Lightning > Lightning Bolt at 80 for MW5 even for 1 mob...
Damage at 80 715-815 (plus SP)
Damage at 80 973-1111 (plus SP) first target (70% of damage to sec target and 49% to third target)
They scale differently with Spell Damage, so Chain Lightning won't hit as hard on a single target as Lightning Bolt will.
There's a reason Enhancement Shaman will ONLY use CL on an aoe pull (if they don't suck anyways).
Quote from the second page of this very FAQ:
Chain Lightning - 112% (64% + 32% + 16% on each "jump" respectively)
Lava Burst - 57.14%
Lightning Bolt - 79.4%
Pay attention to how Chain Lightning breaks down. It has 64% SP scaling on the first target, while Lightning Bolt has almost 80%. Big difference.