Also, maybe somebody could do the math and check the value of simply using Glyph of Disease to cut out IT/PS if your rotation. At the moment, it seems obvious that you wouldn't want Disease because you need to IT to refresh IIT, and you get that extra 5% melee haste.
Icy Talons is attached to Frost Fever not Icy Touch. Glyph of Scourge Strike & Glyph of Howling Blast provide the Imp Icy Talons buff.
EDIT1: I stand corrected, according to wowhead, Glyph of Disease does NOT provide Imp Icy Talons buff. It only refreshes the duration does not re-apply the disease.