I don't find it thaaat much smaller than the Oly 12-40 f2.8. Personally, the size difference is so small that I'd definitely go with the 12-40 f2.8 instead (which happens to also be better optically).
Yeah, I would probably go with the 12-40 too. Interestingly enough the local Associated Press staff photog is using the 12-45/4 however, whereas everyone else went with the 12-40 (or probably just kept it from before).
I also found a little bit of error in the "Competition" section on the final page. The "Leica DG 12-60mm f/2.8 ASPH OIS" is mentioned whereas in actuality it's an f/2.8-4 lens, an important distinction I think.