I just replaced a RB493G running 4.17 for a RB850Gx2 running 6.27. The configs are the same between devices however the CPU usage has large spikes as you can see on the Usage graph attachment.
If you look at the Normal CPU attachment this shows how the CPU usage is normally .
When I open the device settings page in The Dude I get around 40-50% CPU usage jump for up to a minute that shows up in the Profile tool under Management . This did not happen on the 493G or any of my other Routerboards running 4.17.