I had mine upgrade when mike did his first or second trip doing the full monty. Yes you will notice the difference,it is smoother, revs faster and harder and makes more power, what more could you want
I was working away so my dad (in his early 70's at the time) took the bike down (to Old Son's IIRC) and even he commented on how much nicer the bike was to ride.
I changed from a Quill T3 to an Akrapovic and added a 4 degree advancer, I didn't gain as much at the top end but even more in the midrange.