which way to go?

Do you have time to make the detour out to Mitchel falls i suspect not
I say do the gibb but before getting to derby after napier downs take the good road south to the GNH which takes in geike Gorge (small detour) windjana gorge and tunnel creek
Alternativly if you take the tar do this road Hooking up with the gibb close to Derby

In the same situation I'd probably leave the Kimberley for the next trip (there will be one of course, won't there !). The Kimberley is fantastic and there's heaps to do and see - you could do the Bungles and then scoot off to Derby in a much shorter timespan. The Bungles are brilliant - the narrow gorges on the northern side are best seen around mid-day, to take advantage of the vertical light - very impressive sunlit chasms. The southern beehives section might be best in the am and the pm - a bit harsh around mid-day. Chopper flights operate on this latter southern section.