I bought an 066 over the other choices...
Although it doesn't have the torque of the 075 I was looking at, it also weighs significantly less, and has adequate power for the stuff I've done to date. Sure, more would be better, but, I often have a bit of a hike to get to the log, and the 075 was just too clunky for my situation.
I haven't used anything but the 066 on my Alaskan, but have been quite satisfied with the choice. Of course, I only mill 4-500 board feet a year. Not that I don't lust after an 088, I just don't want to carry that hoss around.
I haven't had the spreading problem, but my bar is on its last legs, it was well used when I got it, and will be replaced when my ripping chains start looking stressed out, if not before.