Is there an actor-per-scene limit in PhysX 3.x?

I remember PhysX 2.x had a hard limit of something like 40,000 actors per scene. And also a different limit on contact pairs. I can’t find a mention of these limits in the 3.x reference, are they still there?

It was mentioned in Release Notes, that win/linux SDK (3.2.1 and above) supports a maximum number of 4294967296 contact pairs

Right. Well if this is the only limitation, I guess it is up to us to estimate how many actors of a certain type are likely to exceed this number of contact pairs.
By the way, what exactly would happen if this limit is exceeded?