Well I think thats a comprehensive out flank and encirclement by me. Having been wrong about the lens mount you fudge a change of direction.
My first instinct would be to suggest that if the sensor needed to be moved 4-5mm by the image stabilisation, then a tripod should be used
And when shooting from a car, boat, or airplane, a tripod would accomplish what? Or what about shooting in venues where tripods are not allowed? Or you are shooting from a tripod, and there is a strong wind that is still causing camera shake? I've encountered all of these situations when shooting.
You still have said nothing that refutes my original point--that body-based IS becomes less effective as focal length increases, because the mirror box/lens mount imposes a hard limit on how much shake body-based IS can correct. And longer focal lengths are where IS is needed most.
Yes, the outer diameter of the Olympus mount is somewhat larger in proportion to the sensor size compared to Canon's lens mount. But that still imposes a physical limit to the effectiveness of Olympus' IS system that does not apply to the Canon. Focal length has little effect on lens-based IS system's effectiveness. With lens-based IS, the corrections made by the IS mechanism are magnified in direct proportion to the focal length of the lens, so lens-based IS is equally effective at all focal lengths. But with body-based IS, the distance and velocity that the sensor must move to provide a consistent level of shake compensation increases in direct proportion to focal length, and the hard limits of how fast and how far the sensor can be moved impose a hard limit to the maximum focal length at which effective IS can be achieved.
With lens-based IS, if you have a 600mm lens and add on a 2x teleconverter, the lens-based IS will be just as effective; if IS was eliminating 80% of the shake before adding the TC, it will continue to eliminate 80% of the shake afterwards. But with body-based IS, the limitations on the distance the sensor can travel and how fast the sensor can be moved will reduce the percentage of shake that can be compensated for by the mechanism. If the 600mm lens is already causing the body-based IS to work at 100% of its capacity to reduce shake by 80%, then adding the 2x converter means that the body-based IS mechanism will only be able to reduce shake by 40%.
Since I don't have an E-3, I can't test to determine the focal length at which its IS mechanism is operating at 100% capacity in terms of sensor movement speed and travel distance. But the effectiveness of it's IS mechanism in reducing shake beyond that point will fall off dramatically, with the percentage of shake being compensated for decreasing at the same time overall shake levels are increasing.