I had the opportunity last summer to see a similar sized turbine jet. It was really amazing to look at and see all the craftsmanship that goes into something like that. Unfortunately I had to leave as he was getting ready to fly it but I heard it flying over.
O.K. For us US guys, 500 Km/h is just over 310 MPH, or close to .5 Mach or almost half way to the speed of sound. That is so fast for RC control from the ground. Would be something to watch for sure. Wonder how long before someone claims the speed of sound in RC planes. With turbines the power must be avaiable. Not sure it would be a good thing for the hobby but it is coming I suspect.
and also someone needs to make a seriously strong airframe. I bet if you have a strong enough airplane and just get it up to altitude and dive it, you can break the sound barrier. That would look so so cool! probably FPV too. I would think a 770 mph model would be pretty darn hard to see.. Technically, the first breakings of the sound barier were with planes in steep dives, so it would sort of count as breaking the sound barrier in dive. and then from there move on to breaking the sound barrier in level flight, perhaps first with rocket motors with long burn times, like the Bell X-1.