The logic boards were identical in the Q650 and 800, so it sure ought to be impossible to tell them apart. At the sales counter, you'd be asked, "Do you want that on your desk, sir, or on the floor?" Depending on your consumer preferences, they'd cook up either a tower 33MHz 68040 or a desktop 33MHz 68040, and serve it up, piping hot, in your preferred location. Simple as that.

I suppose that one advantage of the Q800 form factor was that you could get an 8100 board in it (with a new backplate). The same surgery was possible on the Q650, but then you only got a 7100. 8100s were the high-end machines.

I have also found the Q800-840av/ PM8100/ PM9500 series to be admirably quiet, whereas the desktops make a fair bit more noise. It must have something to do with the power supplies and air circulation....

Some find the desktops uglier than the towers, but I rather like the form of my Q650 and IIvx. The curve on the front was one of the signature themes of Apple design right up to the time of manufacture; the air intake at the bottom of the front on the machines is especially classy: no mere grill, folks, but an elegant curve complementing the overall design. To my mind, the case design of the towers is redeemed only by the "feets" motif; otherwise, the tower design is rather unimaginative; they are also, as is well known, a pita to work on. But they were quiet machines in daily use, that has to be said.