I remember having trouble getting first place on Moa Therma while going for Arcade Perfect using AG-S, I switched to Icuras and got it almost straight away.
Maybe the specs for a crafts Top Speed only really come into play when racing against the AI.
When racing online or 2 player split screen these supposed speed differences might actually be compressed to a smaller difference in speed, or negated all together, it's just the handling that remains different.

I suppose Colin Berry could answer this one.