The most important thing for the 64T is the processing. I saw the 64t processed by a lot of European laboratories and the best result (really great) comes from Fotocinema in Rome.
http://www.fotocinema.com
http://www.trinityweb.it/fotocinema/super8.htm (clik on "pellicole" - bottom - to see the prices)
By the processing of this laboratory, sharpness, colors and gamma are better than the K40. Expecially the sharpness is better. The grain is a little bit more than the K40, but less than the processing by others.
I suggest to try the processing by Fotocinema.