The changes to the internal field stops were well documented on some German optics forums (Juelich, if I recall), and included improved baffling also. Likewise, there have been two different German magazine tests over the years that had measured transmission values, the first an early one, from the first few years of this model, and the latter from some four-five years back. There was about 5% increase in transmission between these, and I saw the difference readily in my now-sold early model and my current late 2010 model. I haven't done comparisons between my present Canon and the latest production units, but will try to do that sometimes this fall.
I don't recall the exact figures from the tests, but it was something like 83% daylight transmission in the early one and 87-88% in the latter. So roughly like from first generation Ultravids to Ultravid HD +.