Never observed with the 2013 MacBook Pro, and both wired with gigabit ethernet—
The 2016 MacBook Pro regularly does a rainbow beachball for a second or two, then all is well. It seems to happen if the machine has been idle for a bit, but not gone to sleep. In three years I (Lloyd) have not observed anything like this behavior with the 2013 MacBook Pro.
The cause is unclear: could it be related to some kind of new power management algorithms? It’s minor but annoying, along with the chimeless black screen guessing game at system boot. These two behaviors constitute annoyance only, but they are surprisingly irritating compared to the rock solid predictable behavior of the 2013 MacBook Pro.