What can we learn from Vettel's success in Jerez?
But not this time - an informed source tells me that Vettel's 1.3-second gap to the next fastest car (Felipe Massa's Ferrari) on Sunday cannot be fully explained by the fuel load he was on. In fact, only about half of it can.
In theory, that means that, at least on Sunday, Vettel's car was something like 0.6secs faster than a Ferrari.
And, yes, lap times in winter testing are notoriously inaccurate guides to form. It's impossible to know what specification the various teams are running in - and a lower fuel load, new tyres, and even the time of day can all make a huge different to a car's speed.
But this information about Vettel is in the context of a pretty reasonable knowledge of what the other teams were doing.
And that means Vettel's performance confirms the increasingly prevalent feeling that Red Bull could really make an impression this season.
An insider at the team tells me that a secret test at Valencia last week went very well and that the car is "looking good" - and that is not just a reference to the fact that it is undoubtedly the most beautiful of the 2009 cars.
That, the insider says, does not mean they expect to be challenging McLaren and Ferrari for regular wins - just that they might have a chance of being best of the rest.
Looking at Sunday in isolation, though, you wonder whether that might be an understatement.