With the cat in the stock location, it's traditionally accepted that 4-2-1 allow for more midrange torque while the 4-1 helps with high-end. The very best setup NA, as I understand it, is a 4-2-1 with extremely long primaries (ie just about as long as the standard 4-1), and the cat is pushed back about a foot or so to allow for the 2-1 convergence.

With a supercharger, you want a 4-2-1 with extremely fat and short primaries.