So, i thought after posting my horsepower challenge, lets do a speed challenge, this is my entry.
Are we talking greater than 0 reliability, or max theoretical speeds? If it’s the latter, I guarantee you I won’t bother to find the absolute max, but I’ll at least up the ante.
I am 99.9% sure that higher ‘theoretical’ speeds are possible, but this should set a bit of a ballpark.
EDIT: case in point, I changed tyres and now the value is 727.0.
I was going to comment just before this saying something along the lines of “Yeah, you’re not even close to Strop & Vosnox’s records” 
Just playing along. No point pursuing higher top speeds until devs increase the maximum gear ratio so we can plonk our 3000+ hp engines into cars and equalize our power peak with the theoretical top speed indicator.
Moved into Challenge section.
I have a feeling these top speeds will be annihilated by the introduction of V12s.