I find commuting to be an interesting beast in this city... like conundrum, I have Joe Rocket Alterego pants, but I have a Joe Rocket "Champion" Yamaha Leather jacket. They both have the 8" zipper along the back to zip together, but they don't actually zip together (no big deal).
My jacket fits very snug with a hoodie/sweater on underneath (over a t-shirt), and a little loose with just a t-shirt on - also the "thermal liner" in my jacket is just a vest, not full sleeve, which I like. Ideally, I'd like to buy another leather perf jacket for hot weather rides, for the above reason, but this'll do for now. I LOVE my jacket because it has zippered vents, and I honestly can't fathom spending money on a jacket that doesn't have at least 6 vents (2 arm/pits, 2 front and 2 rear, like my current jacket). Based on my needs for pants at the office (and how cold it is), I'll use the Alterego pants over "nice" work clothes, or if I can get away with jeans, I'll wear one of a few kevlar jeans that I have.
Basically, my tolerance for cold and fitment of the jacket results in the following usage:
<9C: not riding
9C-15C: sweater on, thermal liner in, vents closed
15C-20C: layers same as above, vents open
20C-25C: thermal liner out, sweater on, vents closed
>25C: thermal layer out, no sweater, vents closed or open as necessary.
Venting is sooo important, cuz on a typical day, I'll ride to work in 15C, then home in 30C... it took about a year of steady commuting to figure this out, but I can be comfortable in the full range of temperatures for Southern Ontario
YMMV