Yes your kit chain, 415, will fit the sprockets. The 40T will give you a little higher speed but the 44T will allow for better hill climbing. Think of it as gears in a standard transmission car. The bigger the rear sprocket, the lower the gear. Some guys run as low as a 36T in the rear and can get some awsome speeds but their ability to haul up a grade is reduced. The 40 or 44T is a good all around ratio for pleasure riding. Good luck, ride careful.
Tom