There are lots of places where JMP is multithreaded, mostly in the platforms. For example, try Distribution with lots of columns.
You'll see all your processors light up as JMP sends each column to a different thread.
While JSL itself isn't multithreaded, anything that it calls that is multithreaded will use all available cores.
So, multiple cores can make a difference.
As BrianCorcoran points out, the most important factor for performance is RAM. We typically recommend that you have at least twice as much physical memory as the largest data table that you will use. So, a 4 GB data table would require at least 8GB of physical memory.
After that, number of processors and processor speed is next.
-Jeff
-Jeff