Maya is not fully multithreaded. You need very powerfull CPU for sofisticated SubD modelling. But what I use in this case is modeling without displaying poly proxy cage and it is fast enough But if you plan to animate Subd geometry using any deformer or binding it to skeleton, solve this problem on poly proxy base(with animating and other deformers for char. setup) and then bind SubD to skeleton and copy skin weights to Subd from poly proxy model, etc. ... I think you know about these methods enough ...