Race Predictor and Personal Records

The values on the watch are estimations, based on your actual fitness level, while the second table are real results. The predictor does not use your true results, but rather the typical safe performance (without the risk of an injury) for a person with that fitness level.

Short distances' times are close. Maybe not enough data for marathon yet, it should get better fit after more runs.

For me it predicts times which are possible, but require effort.

In the past, the race predictor was based only on the VO2Max estimated by the watch, meaning any two people with the same estimated VO2Max would have the same race predictor numbers. For newer watches, Garmin also adjusts these numbers based on your training (training volume, I think), so you would see a slower number for the marathon if Garmin thinks you aren't running enough weekly mileage, for example. What it doesn't do is make any updates based on actual race results/PRs.

So in your case, it seems that Garmin is underestimating your VO2Max. (I have the opposite experience.)

You might want to make sure that your max heart rate is set properly, as well as weight and age. (Although I've always felt that weight and age shouldn't have any effect on the *estimation* of VO2Max, since the Firstbeat whitepaper explains how estimation is mostly based on the relationship between your heart rate and speed. Obviously weight and age affect your actual VO2Max, though.)