I just watched the 220mph run and unless they have changed the gearing in this car since then I don't think it will go over 238 (provided they are running more power now).
They have obviously changed the gearing from stock (for the 220mph run). He was shifting into 6th at 200mph. They probably did the 3.9 gear change on this car (not good for top speed runs)
I was in 5th at 226 with stock gearing. I never shifted into 6th.
there are a bunch of unknowns on being able to predict a speed for this car.