I thought I'd share my failure so far.
1) Knitted a sleeve for about seven inches, tried it on and was shocked to find it was far, far too wide.
2) Started the sleeve again this time completely ignoring the instructions and decreasing much sooner and much more frequently.
3) Finished the first sleeve and tried it on yet again, only to find that it was actually STILL pretty freaking huge, and the fact that it seemed so much improved probably reflected more upon the fact that the first attempt was ginormous than that the second was actually decent. I stared at myself in the mirror thinking, "I could deal with it... no I can't. Yes I can. No I can't."
4) I'm starting the second sleeve- I managed to tuck in the excess fabric quite nicely and you can no longer tell that it once sagged at the pits and was not cool at all. Of course, with my luck I will knit the second sleeve, sew it up, finish the body, work the border, try on the completed garment and then... decide to reknit the sleeves again! Fingers crossed that it won't happen, but we shall see.
As a side note I rather like the Filatura Di Crossa multicolored alpaca blend that I'm using as the contrasting color. I think it will be rather nice once it's all tied in together with a border at both sleeves, on the body, and the border band. More pictures upon more progress.