Not only that the Toro Rosso is fastest on the test surprises me, but top guns like Mclaren and Ferrari are slower.
This winter tests has been rather strange because of the new Aero rules, all teams are trying different ways of testing. I notice that Toro Rosso still uses the 2008 aero setup with slick tires. They probably do a rough estimate that they will deliberately run at 50% downforce to simulate the new aero.
On the other hand, BMW, WIlliams are both using a completely new 2009 aero. These guys jump straight into the 2009 rules on a white sheet of paper (I speculate). I've just noted that Williams still have some aero stuff on the side of the car.
Ferrari is testing with no barge board. I am guessing Ferrari is removing the extra aero bit by bit and incrementally move to the 2009 rules. Seems kinda expensive and time consuming, but has the advantage of being safe and predictive.
overall, it seems the 2009 cars will be slower by 1 to 2 seconds.