That 1.24 is very close to the 1.26 linear factor for 2/3 stop, but if you prefer the extremes, 1.15 is 2/5 stop and 1.3 is 3/4 stop. (A factor if 1.4 is one stop.)
(I used 22.5x15mm for EF-S, but recent EF-S have the slightly smaller dimensions that you gave.)
Let's not quibble. Let's call it 2/3rds of a stop advantage. Moving on to the ramifications of the greater DoF of the 4/3rds format, I think we are all searching for the sort of performance in the lighter camera that can equal the performance of the heavier model.
How would a G1 with 14-54/F2.8-3.5, or 14-42/F3.5-5.6, compare with a 50D with EF-S 17-55/F2.8? Where are the tough comparisons?
It seems to me that a 50D at 17mm and F3.5 might produce a cleaner and sharper result than a G1 or E-620 at 14mm and F2.8. DoF should be about the same, but in low light I suspect the 50D will surpass the 4/3rds format.
When DoF can be sacrificed, or when a shallower DoF is desired, the 50D at 17mm and F2.8 will outperform any 4/3rds camera and lens combination, I suspect.
A 4/3rds format lens equivalent to the EF-S 17-55/2.8 would be a 14-44/F2.2 across the whole range. It doesn't exist.
If we compare the 4/3rds format with full frame 35mm of the same pixel count, for example, the Nikon D700 and G1 or E-620, I suspect the gap widens. With a 2 stop difference in DoF, I'm prepared to accept that a G1 or E-620 at ISO 1600 might be at least as good as a D700 at ISO 6400 regarding noise, but where's the equivalent Zuiko lens to Nikkor 14-24/2.8? It would need to be a 7-12/F1.4. The closest is 7-14/F4.
Another issue is of course resolution at the DoF equivalent F stop. Is the Zuiko 7-14 at 7mm and F4 sufficiently sharp to compete with the Nikkor 14-24 at 14mm and F8? If it is, is it also sufficiently sharp to compete with the Nikkor 14-24 at F4 and F5.6 in circumstances when a shallow DoF is okay?
If a Zuiko 7-12mm/F1.4 were a feasible proposition, woulkd it be about 50% sharper at F1.4, from corner to corner, than the Nikkor 14-24/2.8 at F2.8.? It would need to be to delvier equally sharp image resolution at the 12mp level.
I don't wish to appear dogmatic about such issues, but the great dearth of direct and competently executed comparisons on the interent give me reason to suspect there's really no contest.