Always take the HoX specific gear e.g. don't forgo the strength and combatrating for a meager increase in spelldamage.
Compare T4 HoX and T4 caster chestpieces:
HoX-Chest
Caster-Chest
HoX gets you slightly more hit and critdamage which is outweighed by the pure int (and thus Critdamage from WotS-Silverperk, str on HoX gear nets you critdamage as well) on the caster chest.
HoX chest is behind on magic damage by 14 points, but in turn you get 72 strength and 300 CR(2H).
These 516 CR will increase your dps far more than 14 magic damage.