I find my club's course to be just about ideally comfortable given my current distance. It's 6,200 yards and that implies a driver distance of around 221 yards. I do hit one or two drives longer than that most rounds but much more common is a drive around 210-212 yards (but that may be because on many Par 4 and some Par 5's I land on a ridge or upslope). Then again, the 64% thing would imply my 6-iron goes about 142-145 yards and it consistently goes half a club farther than that.
Still, it's in the ballpark. Easy to believe that my "ideal length" is 6,000 but that a familiar 6,200-yard course is easy enough. I sure don't mind playing under-6,000 courses though, I'll tell you that! If I had a true "ideal" it would be something around 5,600-5,700 yards, Par 68-69. I don't reach the Par 5's in two anyway so a course with, say, five or six one-shotters, a dozen two-shotters and at most a single three-shot hole is great fun and an easy walk. That's my ideal.