I got the 750 km number from:

 

http://en.wikipedia.org/wiki/List_of_Solar_System_objects_by_size

 

Maybe I phrased it improperly, or there's something that I don't understand about the way they're using the term "hydrostatic equilibrium".

 

Rhea Saturn V		764.1	smallest known body in current HE
Iapetus Saturn VIII		735.6	largest known object not in current HE

I'll research this, and see if I can't figure out what I'm actually saying here.

 

Ultimately, these numbers could be cross-referenced with the depth at which plasticity is achieved inside the Earth. The distance is a lot less than 750 km, and more like 40~70 km (i.e., the bottom of the lithosphere). But the gravity, and thus the pressure, should be the same.