I personally believe that McLaren is making a new diffuser, but are not willing to show it till the first race, hence the 08 rear wing... people have been saying that D/F to Drag coefficient can never be simulated by the 08 wing for it has a larger surface area. But... I was just thinking and this is my opinion, maybe they have designed a diffuser that could counter-act the drag coefficient of the 09 rear wing. I don't know it's all open for me... It is either McLaren is having a big problem or they're just keeping their cards to themselves...
What would the McLaren engineers do when they saw Newey's design of a diffuser, after Williams and Toyota, had theirs legalized... THEY WILL IMPROVE IT.
Hence, I think the last day of the barcelona test is the most important... unless it rains... again... F1 is starting to hate GLOBAL WARMING!!!