To answer my own question, I have searched around, and I have found some information on floorspace over at Urban DB.
Commerce Court West:
Floors: 57
Height: 239m
Floorspace: 108,528 sq.m
Bay-Adelaide Centre 1:
Floors: 50
Height: 218m
Floorspace: 107,054 sq.m
RBC Dexia:
Floors: 41
Height: 185m
Floorspace: 111,500 sq.m (office only)
Telus:
Floors: 30
Height: 160m
Floorspace: 75,251 sq.m
I'm using CCW for the comparison because it seems to be the most similar (and also because I work there). So, CCW is the tallest of the four, by about 20 m. It's also the second largest, in terms of square meters.
Now, consider this for a second, right now, we have under construction in the downtown core, three office buildings which will be done around the same time and which are the equivalent of adding 2.75 CCWs. That's insane.
I'd love to see what these additions do to the total office space figure for downtown Toronto. And, I'd also be curious to see how Toronto stacks up against Montreal, Calgary, Vancouver, Chicago, Atlanta, and Houston. Anyone have some numbers?