Driving impression: John Deere 7500 ProDrive forage harvester Differential lock, food for stock – plus loads of smoke from its barrels With its Claas and Krone rivals galloping along the harvester highway at a brisk 40km/hr, Deere’s 20km/hr SP forager has been looking decidedly lethargic. But this is about to change. We take a drive on the John Deere ProDrive, which debuts in the UK this year before going on full commercial sale for 2007