Yes I can confirm that your code works perfectly on my setup both with, and without the two lines relating to serial.
Connecting all the servos to PWM/Non-PWN pins didn't solve to problem, two of the there servos are still jittering. They are wiggling with a mac deflection of about 15 degrees both ways. They do however rotate to the general angle specified by the transmitter.
I have also tried removing Serial code from the loop, but leave it in the setup function. The issue didn't go away suggesting it have something to do with printing the values to the monitor, and not with general Serial functionality.
Also, thank You, for taking your time to reply and document your findings for other people. I thought I'd never manage to thank someone who inspired be want to become an engineer