There was quite an interesting youtube from Engineering Explained speculating it had enough power to do 400 mph. There may have been other constraints limiting things like the tyres being safe and apparently the battery only has capacity for 2 mins at full power, plus bits may overheat and the like.

(https://youtu.be/z6q7du1q2U8)

It's also interesting that the fastest time on the Nürburgring at 5 min 19 was from a Porsche hybrid with 900 hp, a fair bit quicker than the BYD which took 6:59 I think. The Porsche had a lot more downforce than the BYD.