"As of today, this is the best car I've ever had," the Spaniard, who won the world title in 2005 and 2006 with Renault [ Images ], told reporters after the penultimate pre-season test ended on Saturday.
"Red Bull, McLaren [ Images ] and Renault have been very quick and have shown their cards, while we are still hiding ours," he said.
"We will analyse the data, but we are very optimistic. As of today, if I were in a different team I would be looking at Ferrari because everything is going really well.
"Maybe where Ferrari has to improve is the short runs with little fuel onboard."
The final test takes place at Barcelona [ Images ] next week before the season-opening race in Bahrain on March 14.