The two models are extremely similar, in both design and configuration options, with some accommodations for needs of the x360, such as hinge design and display technologies.
They adopt some of the slicker aspects of the Spectre and EliteBook lines, such as the milled aluminum bodies, while remaining more durable. I expect to see a lot more of these unworkstationlike mobile workstation designs this year.
Although it looks quite thick folded into tablet mode, the hinge is what produces that effect. The ZBook x360 is really only about 0.1 inch (2mm) thicker than the consumer Spectre x360. As you'd expect, a Xeon plus Quadro requires more space for cooling airflow.
HP is in love with chamfered edges this year. It's not my taste, but it achieves the industrial look HP probably hopes people will equate with workstation power. The x360 looks identical to the ZBook Studio G5 in clamshell mode from this angle. Unlike the more meat-and-potatoes models, the Studio keyboards don't have extra buttons on the touchpad or a joystick embedded in the keyboard.
HP changed the look of the speaker grille. Also, the G5 ZBook keyboards now include dedicated keys for conference call controls -- connect and disconnect -- plus a button for jumping into presentation mode.
The Studio models have an option for a 600-nit, Adobe RGB DreamColor 4K display. Also, note the thinner bezels. That's a consumer trend that's finally starting to make its way into mobile workstations.