Cruising on interstate 89 I happened upon a 2005 530i. As I approached, the driver stepped up the pace so I went along for the ride. Around a big sweeper at the base of a mile long hill near Montpelier, about 80% grade, I dropped to 4th and passed. I could see him react as I went by and managed to get about 15-20 car lengths ahead. In 4th up to readline then 5th, to the floor. Then, he started creeping up on me. I panicked and went back to 4th... I was already well into the redline, back to 5th....135mph on the dial. One eye on the tac/speedo and the other in the rearview. He's still gaining, reeling me in. We were coming up behind another car as we crested the hill, so I let off a little and changed lanes. By then he was just 5 car lengths behind and then peeled off at the exit a the top of the hill. Man, this is first time I've almost been manhandled by another vehicle with the M5. GUYS, where can I get a little more horsepower for the next hill climb/street fight? This whole thing made me a little quezey. But better another beemer than some other 'thing'.....