Many thanks for your suggestion and support for TrainingPeaks Virtual.

TrainingPeaks Virtual uses a real-world physics model for all it's dynamics and so the speed you go in the app should be identical to the speed you go outside, if all of the data going into the model is the same. This has been extensively tested by 3rd party tests and found to be very accurate.

Potential reasons why there may be a difference to what you are expecting though include: A difference in Crr (perhaps the roads in TPV are smoother than the ones you ride on normally), a difference in CdA (perhaps the bikes, or your riding position, in TPV are more aerodynamic that how you ride normally) or of course wind and/or drafting (perhaps you were in a tail wind and/or in a strong draft behind other riders).