That's funny, the Shak in a L fits me, but the L Carrie is just too sloppy through the shoulders and armpits (and I have broad shoulders). I ordered a M to see if it would work, but it may be too small. I can't really figure out Ibex sizing; it seems like every piece fits differently.
I agree about the zipper making the Shak look casual. Luckily my office allows casual dress all the time, but I may limit the Shak to Fridays.