AG,
I have heard other GCA types say none to 8,000 yards. I still see several routing proposals from architects, including Tom Fazio, who favors playability over tournament tough under 7000 yards.
As to architect input in total length, my experience varies from having no input - the Owner says he wants X yardage to having total control. Personally, Most owners still are asking for a minimum of 7000, and I have only had one call to design something over 7,500 yards. Left to my own devices, anything over 7000 yards from the tips still works for me.
I sense that the "new" benchmark for a "championship course" is at least 7200 yards, since my last four courses have each, by some miracle of chance, or creative measuring, have come out to 7,201 yards. I suspect the courses are really 71something yards, and the DOG thinks 7200 is the magic number, so they measure from the very back of the tee, instead of two paces off.
That is certainly plenty to convey the image of a "modern" challenge, while not being so long as to be unplayable back there for the good players. Even the pro tour guys complain when courses get much over 7300 yards, as being too long for some of them.
Although some architects disagree, I don't see the real rush for length that others do. While I do see the need to lengthen courses, since even average players are driving past fw bunkers of just a few years ago, very few can play the back tee yardage anyway. Those that do still like a reasonable challenge, which 7500 yards and up doesn't provide.
In short, unless I know that there WILL be some kind of tournament, I don't see why we have to build really long golf courses.