Steve said this fall that they were going to be able to use the S62 for the first part of 2011 season, and then they are being required to shift to the S65.
Here's what I wrote in another thread last fall:
It was great to hear him talk about the development of the S62. He's found a lot of power in the S62 mainly through extensive and creative engineering, eliminating frictional losses, etc., all proprietary. Since in the Rolex series, you have to use the stock intake system (i.e. throttle bodies, intake trumpets, plenum), stock valves, etc, he didn't ever think he'd find as much HP as they have within the engine in the past couple of years.
Next year they have to use the S65, and he didn't sound too excited about it since the largest displacement they can get out of the S65 is 4.5L. He thought they could get close to the same peak HP out of the S65 as the S62, but they'll have to rev it about 1500-1700rpm higher resulting in more pumping and frictional losses. The only pros were that it is slightly lighter and smaller, so it can be placed a bit lower in the chassis, and they'll have some small amount of ballast they can place appropriately.
Chuck