Personally most the time the set bonuses are more benifical then a few extra stats, though sometimes the 4 set isn't that good.
It also depends greatly on how you play and how often you use (can use) the abilities the 4 set bonus enhances.
In your case i would stay with 4 set bonus and wait till you can get the 2 set bonus, either that or go get the hands for T8 (so you have all 5) then have the helm, but this probabily wouldn't be worth the hassle.