I can safely do it in good conditions in six hours and I'd consider myself a very experienced driver for that route, having driven from Skye to Glasgow or Edinburgh and back a couple of times a week for years.

Absolutely, doing it in half that time would be madness though!

Doing it in half the time would be impossible. To travel 250 miles in three hours you'd need to keep up an average of 83mph-ish for the whole journey.

I shouldn't think there are many places you can reach a peak speed of 83mph for long on the whole road.

Some lunatic will take it as a challenge :-) (and become a statistic)