The set bonus for custom gives 2 crit and 6 damage as well, which is the real benefit of the custom set. It ultimately boosts the minimum range of attacks by about 10%.

My mind wrack crits with full custom have exceeded 150... It was very much a good investment, as 50 health is about a 15% boost in survivability, which is needed because if you go all out on a boss with amplify pain and precision, your tank will not be able to keep aggro!