I have a "barebones" Ultimate (64) installation on one of my laptops, purely for comparison purposes. It takes up just under 14Gbs. In use, making allowance for hibernation files, increasing prefetch size and pagefile use, it quickly swells to 18/19 Gbs.
But that, of course, is only a part of the story. Allwance has to be made for your own programs, possuble extended use of homegroups and add-ons/saved requiements of your installed programs.
Unless you are a dedicated game player, which can eat up disk space, I would also agree that 60 Gbs would be ample under most circumstances.