Just installed a new FMF Powecore 4 on my TW. Standard couple of turns out on mixture screw, a few .010 shims on needle and a 130 main jet. Along with my recent change to Mobil 1 oil my engine purrs like a kitten but it does have a bark. It's a little loud for my taste and I have the quiet insert on order. The bike now has more torque throughout the throttle range - less downshifting in all gears but especially noticeable in fifth gear cruising uphill.
There is definitely more potential in those little engines than the way they come from the factory!