The difference between the rev3 and rev4 is significant. I would doubt that it is just the age difference. I can get the rev 4 filter EG to match the rev3 by applying poly mod from the filter to the filter. So, having the filter eg modulate/multiply itself. Even then I have to set the poly-mod amount to 25%. Maybe that is a fine work around.
I did contact customer service and they said this was to be expected. The rev 3, with filter in self-oscillation, will go above hearing range when the filter eg reaches the top. I can't do that with the rev 4...perhaps I just happen to have a rev3 with a hot filter eg??