No, 100% OE is supposed to be that : you are stretched to your limit, you are not supposed to go further. I never tought of going above that number, and I think the fact it is a percentage and has all those nasty modifiers attached to it shows that, even if you are able to temporarily go above that, you shouldn't. It's like FL.
However, and I am not sure if it already does that, OE should scale better with the size of your empire, so that eating a few provinces shouldn't put you at 100% OE as a big empire, but should totally do it if you are a medium power eating a third of a country of your size. To summarize, I think that the effect of corruption on OE is fine, but OE itself should be nerfed so that 100% is close to doubling your size.
That way, you would have a snowballing effect which can be stopped since you would experience a period of vulnerability if you go too far too fast with your expansion.
I would rather not slow down OPM expansion. Slow =\= challenge remember
- 2