I am assuming you are posing this question as it pertains to DPS, and not tanking. I will answer for both scenarios, just in case.
As a DPSer, I prefer Glyph of Howling Blast and a single Disease build. For this, Epidemic is a waste IMO. I have the Relic from XT though, and it allows me to focus more on Frost Strike and less on Obliterate for my Damage.
As a Frost Tank, you probably shouldn't take IIT at all, leave it for the shaman or DPS DKs to pick up.