I believe that was the case a few years ago when we were debating Unix v Windows servers. Mind you, it was difficult to get a level playing field, as the Unix boxes had Motorola processors which were much faster than the Intel equivalents on the Windows boxes.

I don't think I have read anything on the subject for at least 5 years now, or seen any true like on like statistics.

Another factor was probably that earlier versions of Unix certainly had less GUI bloat than Windows.

It would be interesting to see some current data.