I think UI which moves with your head is generally an anti-pattern in VR design.
Stuff which is either part of the world, or that you can bring up at the position of one of your controllers works far better in practice.
The Solus Project does a pretty good job with that despite not being made from the gorund up for VR.
Yep, the concept of a HUD based UI is kind of a holdover from traditional gaming where looking around is far less natural, and the only thing you can control. In VR it's better to treat interfaces as parts of physical objects instead of intangible persistent HUDs. Basically diegetic interfaces.
For stuff that needs to be seen at a glance, it's best to interface the information with what's in your hands. Take Raw Data for instance. Pistol ammo is displayed on the gun, and thus always visible when using it. You can also ascertain your ammo level by looking at the side of the gun and seeing how many bullets are left in the magazine. Meanwhile other traditional HUD elements are attached to your wrist. A quick glance like checking the time on a wrist watch is all you need. (Speaking of wrist watches, Climbey uses one as a level timer.)
Then for more verbose things, there's the interfaces which are part of the world, but not locked to your hands. H3VR has a number of those. The item spawner which is a fixed item in world space, and spawnable options tablets which can either be held and put down like the real world, or set to magically float wherever you let go of them.
If a game
really wants to do a UI where the information is virtually superimposed in space rather than be part of an object, then you'd want to emulate AR within VR. Gaze based information that pops up around objects as you look at them. This is kind of clunky at the moment though and will only really be a good option when we get eye tracking IMO.
Here's a question...
...would a G-Sync HMD display be beneficial?
No. In VR we want a new (or virtual) frame every X ms. We want to stop the render when it goes over time and get
something out there. That's exactly the opposite goal of G-sync which wants the monitor to update when the card is done rendering.