Re: New build, Racer.
Oh, pacing will be better than trying to time between two points, as far as accuracy is concerned. It's just that pacing is most accurate when the two vehicles are close together, and considering you'll want to be close together for a long time so that you can wind out to top speed, that introduces a risk of crash. Not saying don't do that, just be real careful when you do.
Even better would be a GPS speedo on a smart phone. The apps can be found for free and should record a top speed.