When the tracks allow it, the Railjet goes over 200 km/h. Vienna-Linz only takes 1 hour, which is about twice as fast as by car. Same for the new Koralm track.
I agree that regional trains are often painfully slow. But that's also because there are so many stops.
Vienna-Graz is mainly slow because it has to cross the Semmering mountains and the tracks date back to the K&K days. This will change with the Semmering tunnel.
