I don't think you're ever going to reach haste cap, so that shouldn't be an issue? ;o
With Icy Veins it's pretty easy to reach 1sec gcd even without frost armor. I have 19% haste and when I pop Icy Veins I get 50% which is the gcd haste cap. So it seems like it is an issue ;p . More haste than that is gimping your damage in Icy Veins cause you can't spam lances any faster and they scale only with intellect. The value of haste in general is obvious, but what about mastery? If you play against a combo that you can consistently stack icicles isn't mastery better after getting gcd capped in icy veins?