All good points here.
My .02 in a nutshell: The "C" rating will affect how "punchy" a battery is, and while other factors do apply, in general your top speed is more a result of the voltage of your pack.
It's also true that C ratings are very subjective to who they are coming from. C ratings are OK for grading packs between the same manufacturer, but as stated by another member the C rating in general is a gray area at best.