I raced KTM's and Kawasaki's during that time..but one of my best friends had both the YZ250 and YZ465. ( We both ran 250 ex and open ex class and also practiced together so I had chances to ride that monster ). I remember that big YZ was fast enough and very reliable but had a lousy rear suspension relative to my KTM's. It pounded the crap outa him. With money they could be made to work well and my bud spent a ton on it. Even so, I could always get inside those things on turns. He got an entire season on that Yamaha with no problems that were because of Yamaha, and then sold it for a Maico. That Maico sprung him loose and he gained 3-4 spots in our class.
I remember that YZ465 being heavy, powerful, reliable, hard to turn, and brutal in general. I liked his YZ250 much better.