Lacking real wind resistance and actual labor of moving 4500 pounds of automobile down two lane blacktop, dyno numbers can be decieving.
You can wind up an MM on any dyno, monitor gross RPM, calculate tranny and rear end gearing, and pencil in a top speed number with grade school math. But, that doesn't tell the whole story.
Neither does peeking at your MM speedo once you're into the triple digits. It's a digital/electronic signal sensed from sensors and sent to a dashboard that has been taught to act like an old school analogue speedometer. Moreover, your eyes have been taught to take a "snapshot" under this kind of real time pressure, and it's all very subjective in the aftermath of 100+ MPH drives. Both you and your MM speedo are more guessing than not. It's a lot like a crime witness/victim giving a cop a decent description of a criminal/offender. It never really matches, but it's close enough.
A Davis CarchipEX will record and download a permanent record of your top speed, and a whole lot of other neat OBDII stuff you can print out for later review. It's also very good for recording long road trips, and documenting vehicle use for business. Fleet managers (and worried parents) love them.
www.davisindustries.com
If you want more instant, but not recorded data from your EEC, take a peek at the ScanGauge. It monitors and report live OBDII data, one of which is your actual speed as reported by wheel sensors to the EEC, and without the springy, bouncy stuff your speedo produces while you are trying to memorize that with both hands on the wheel, tunnel vision mode ON. One glimpse, it's stored in your brain, done deal. This gauge also monitors several more critical OBDII feeds and live too, you can program up to four at a time on your display. Trust me, it's easier to feed your brain this data, than it is to watch MM dash gauges.
www.scangauge.com
One last recorder, is any GPS device. I've used the StreetPilot III for one season, and it has great travel log data capabilities, but doesn't record for download. Still, it's most accurate in actual speed, actual top speed, and a few other neat things you may want to know just about 3 non-stop hours behind the wheel. I'm sure any GPS can do this, and it's all free, you just have to buy the toy you like.
www.gpscity.com
There are lots of ways to look at this 411, hope this helps you find the one that works for y'all.