I didn't think my record was beatable, but you did it, nicely done! There is one issue though, and that is that in vanilla, the floorless and standup trains don't have access to the launched lift hill. This means that in vanilla the record would be 389 km/h, which is still faster than my old record.
A while back, @LordMarcel96 posted a video of the fastest coaster possible without cheats. I've now found a faster coaster. Since steep drops can gain more speed than vertical drops of the same height, I figured that there could be some speed gains to be made if that extra speed isn't negated by the slight extra time spent on the drop. This is also how I created a perpetual motion coaster.
OpenRCT2 allows twister trains of up to 8 cars but RCT2 only allows up to 7 cars, so I assume that's why Marcel used 7-car trains. Using 7-car twister trains, I was able to achieve 389 km/h, a 5 km/h improvement over the previous. Since stand-up trains are faster than twister trains, I was able to achieve 400 km/h with 7-car stand-up trains. Then I tried floorless trains, which can go up to 8 cars in both OpenRCT2 and RCT2, and achieved 405 km/h. This is the fastest train among inverting twister trains subject to RCT2 restrictions and is in the attached park.
If we use the vehicle limits of OpenRCT2 instead, the fastest inverting twister train is the 8-car stand-up. A lucky group of guests achieved 420 km/h.
Even faster coaster.sv6