Having done my fair share of flying quite high in a mustang I will say this. To me flying very high in a mustang is as fun as flying low in a spitfire (I have been messing around with flying a spit at no more than 5k lately). The only downside is the long climb to alt.
The mustang really shines above 20k. I'll turn with about anything up there since I have all the air under me to use for e management. It also makes quite a bit of power relative to many of the "good turning" rides at that alt. It's also a bit difficult to run from. If they dive to the deck so be it. I can either let em go and work on their friends who show up to help, or I'll just dive with them. If I get ganged so what, how else am I gonna learn to fly and fight.
Really nothing better than a high alt stall fight, its much different than fighting on the deck.
Zaphod