When 300km/hour is not enough, there are some ideas to create jet-powered aircraft using Shark design, so You could fly 400-500 km/hour according to used engine.

Price-induction jet looks nice for that purposes : 
At Take Off Power, you can get up to 255daN, consuming 80kg/h of fuel for the DGEN 380 and 330daN with 100kg/h fuel consumption for the DGEN 390.

www.price-induction.com

of course - this kind of aircraft cannot be called Ultralight, although its empty weight could be  very similar