I guess it could be the emulator. Perhaps true PS1 copies display the true speed? Either way you must be going at least 500kmh on average, not 280.
The last thing I remember from myself was around 410 on Gare d'Europa's finish straight
The pal version shows much higher than the NTSC version, even though it is slower. None of the wipeout games have true speed counters as to how fast you are actually moving
Sorry to bring this up again, but I just did some math (exciting stuff) and I calculated that the Rapier craft in WipEout 1 move at roughly 500 km/h.
Here's how I did it: My time trial record on Firestar is 2:08:1 with a lap record of 41.7 sec. Firestar is 6.3 km long. 3 laps is 18.9km dividing that distance by my time is about 0.147 km per second or 530 km/h. Since im using turbos and such we can low-ball the speed as about 500km/h on Rapier.
I can only assume the Phantom craft in 2097 are faster.