The description for the Altmer Elemental Talent is straight-forward:

Elemental Talent (3 ranks) – Increases damage with Cold, Fire, or Shock effects by (2/4/6)%.

The description for Dunmer Flame Talent is less so:

Flame Talent (3 ranks) - Increases Spell Power with fire effects by (1/2/3).

How does that actually compare in terms of increased damage by increasing the spell power?