The damage bonus from stats is percentage based (see
Character Optimization, and in game check out the description of the stats to see their current effect), and an intelligence about 50 would give that bonus.
I generally just looked at the base weapon stats when comparing, though the overall character stat changes could be useful to compare multiple bonuses (ie with low levels of the dual wield skill, your off-hand damage is low anyway, so it may not make any difference to your overall damage if you go with a lower damage weapon with better bonuses).