MSD, can you tell the difference?

Well yes but there are specific improvements. You may pick up 1/2 mile per gallon or so due to the multi spark. Easier starts are a benefit as are lower emmisions.
As far as performance goes,I dont think you'll see much increase if any. Good ign systems are more about reliabilty,ease of maintenance. Look elsewhere for performance upgrades that make a big difference like headers etc.