Mr. Matt, no I have not tried it, it's not really my cup of tea.
Why do I say it's easy? Well, let's say it's easy compared to doing it with a prop, or doing it under FAI rules.
Props and DFs have a very finite speed limit due to the very finite limits of pitch and RPM. I have friends who have gotten over 200 with prop planes, and each MPH over 200 is a serious struggle. It's not easy. If there were a lot of engines that could turn 50k around, it would be a lot simpler.
With a turbine, there is no speed limit to the engine. It will keep accelerating, only the airframe drag is holding it back. You still have issues of flutter and structural strength to deal with, and that is serious but totally surmountable stuff, but the engine is no longer an issue.
I have seen BVM go through the traps with an Ultra Viper at 242. I totally beleive the 255 claim. Put a turbine in that same bird, make sure it will not flutter, and there is no reason why 300mph is not attainable. If someone can get a Hotspot up to 260-something, no reason why a cleaner bandit cannot break that easily. I do remember that those Dutch guys on the AMT website claimed, I think, 287...can't remember what plane it was.