I often used to ferry a 109AII Melbourne - Gold Coast, usually up at FLnosebleed (well, 9-10,000ft: our flight levels don't kick in until above 10k), and the fuel burn would be reduced by 10+%. The cost saving wasn't the point, but the increased endurance was, for IFR flight planning. There are surprisingly few JetA1 stops available in the 800nm trip
Performance was fine, TAS a couple of knots better than 3000ft for the same power setting, but it varied with DA and temp, of course. The S76 would always give better performance at higher levels, with a better fuel burn. Stronger winds at higher altitudes can often provide a better GS, too (or headwind, in which case stay down a bit).
Mind you, Hilico, 200 miles is just a short drive up the road, isn't it?
