you know though, once under load and with wind drag, those cars won't see anywhere near those times or top speeds, right?

The best way to get a good realistic reading is to use an apparatus like a lap timer, with light beams you have to break.

Just like a real car... using a dyno is great, but it isn't going to really tell you how fast your car is going to be once you take it to the track. Weight, gearing, traction, stability, and drag all play major roles in your actual track times and top speed.