Perfect synch is not really possible with existing R/C transmitters. There's always a slight bit of lag, especially if the servos being used are on channels far apart...using channel 2 and 6, for example, in a mix. This isn't due to the processor speed, but the limitations of the radio-frequency (RF) bandwidth.The servos can be updated only so fast before the RF bandwidth limitations come into play.

It's only visibly noticeable if you move the controls very fast, and then you can visibly see one channel with a slight lag. Airplane fliers have seen this also when using two servos on ailerons and/or elevators with mixers. One side moves slightly ahead of the other. It's not avoidable, but also hasn't caused any control problems.