Quote - Maya's 64 bitness mostly exists in mental ray, not the modelling / animation part.

Maya is basically a script shell over a bunch of .dll files which contain all it's libraries (for modelling, animation, dynamics, rendering etc) and they are all compiled with whatever version of Maya they are in. If it's Maya 64, then they are all 64 bit. They may not get any boost from this, but they are indeed as 64 bit as mentalray, or you wouldn't even be able to load them as plugins into Maya. Apps under windows cant run mixed 64/32 bit code, it has to be either one or the other.

And note that large parts of Maya are already multithreaded, including the skinning, IK solver, hypergraph, particles etc. About the only major part not multithreaded is PaintFX IIRC.