Small update and a problem.
The laptop is now 7 months old, and still seems to be a fast as when it was new.
A problem has surfaced however.
On the touchpad assembly, the "left click" button has failed. It still feels and sounds like a click has taken place when you click it, but it has no effect.
I re-installed the touchpad drivers, and in the end did a factory reset from the recovery partition, which brought the laptop back to how it was when it left the factory.
The fault still remained.
The laptop is now back at Asus for repair.