Well, the pitstop times that Shiny posted are not really helpful. The total of time spent in all 3 pitstops are more meaningful. Renault are still ahead.
Code:
Imola
Fernando Alonso 1:11.320
Jarno Trulli 1:11.464
Ralf Schumacher 1:12.206
Michael Schumacher 1:12.719
Spain
Fernando Alonso 1:06.7 *
Jarno Trulli 1:07.2
Michael Schumacher 1:09.1
Juan Pablo Montoya 1:09.8
That would suggest like 1-1.5 seconds or 12-17 liters less for a race distance. (Since the refuelling system is standard, I don't think that technique or tank design really have an importance, not even the 3rd guy who pulls out the hose.)