Don't know anything bout the BF-650. I have a BF-750 and really like the power. Have used it during the winter, when everything was frozen. Sure has power enough to spare. Drug a Yamaha 400 out that had blowen his tranny. He had a Moose in his meat trailer, just left it attached. Tied him off to my lightly loaded meat trailer and headed to the highway, 36 miles away. Really surprised that the BF-750 starts at 18 degrees below zero, without being prewarmed.