There is no chance on hit with
Sigil of the Unfaltering Knight. I think at some point it was a proc, but now the tooltip just reads "Equip: Your Icy Touch will also increase your defense rating by 53." So as long as you keep up IT, you get a pretty significant bump.
I think Death and Decay is recommended as a starter just because it'll snap everything to you immediately, whereas just opening with IT -> PT -> Pestilence means your non-targets can get pulled off you by AOE/Heals while you get diseases up and spread. Would it just be easier to open with a Howling Blast, then start setting up diseases?
I don't normally DPS in Frost, so I don't know what the normal rotation there is.
You can hit the cap with blues and greens, but that's because so much of the "starter" gear is weighed heavily towards defense. My problem is that you can't really use it to build a huge health pool, and that's ultimately what you are judged by. Not that someone with a smaller health pool can't get through Heroics, but there's always a pretty palapable sense of disappointment when a tank shows up rocking 25K HP. I'd rather shoot for something like Defense Cap + 30K HP buffed....once you get into the heavy stamina epic pieces you start to lose Defense rating because items are budgeted more towards parry/hit/expertise/dodge. I could replace my blue chest with Ulduar badge chest and still lose defense. Which is why for the time being I'd rather have that sigil to keep me easily beyond the cap, rather than worry about where I'm gonna make up the +Defense when I get new gear.