"We're gonna need a bigger boat"

This might not be a very helpful answer but, as far as I understand it, if you wish to increase the processing power for 3D modelling you need to get the fastest clock speed plus fastest memory and lots of it, that you can afford, included with a 64-bit system. The processes involved in Rhino and Grasshopper don't tend to lend themselves to multi-threading. Analytical work such as FEA or CFD are very much multi core orientated as is rendering. This is because they are doing lots of the same calculations but in different areas of the model at the same time. Grasshopper needs to be fairly linear in its approach as things at the end of your definition are waiting for things at the beginning to finish their calculations. You cannot jump the gun and split it up.

Now someone else can jump in here and correct all that I've said :)