When you say you are using it with GSync does that mean the Monitor supports GSync too?

The monitor does not support GSync officially, since Nvidia drivers 417.71, Nvidia does officially support Adaptive Sync with DisplayPort:

Here’s what you’ll need to enable G-SYNC Compatible mode if your monitor isn’t certified by NVIDIA:

A FreeSync (adaptive sync) capable monitor
An NVIDIA GTX or RTX graphics card (laptops with internal discrete cards are fine too)
A DisplayPort cable connecting them (Mini-DisplayPort is fine)
NVIDIA GPU drivers, 417.71 or later
Once you’ve confirmed that your monitor is FreeSync compatible and you’re using a DisplayPort cable, check the on-screen menu of your monitor. That’s the one that you activate via the physical buttons on the monitor. Go into the menu and make sure that the Adaptive Sync or FreeSync function is enabled
Now, in Windows, open the NVIDIA Control Panel by right-clicking your desktop and selecting “NVIDIA Control Panel.”
In the NVIDIA Control Panel, you should see “Set up G-SYNC” under the “Display” menu on the left side. If you don’t see “Set up G-SYNC” as an option and you’re sure it’s enabled by your monitor, you might need to install drivers for your monitor manually.
In the Set Up G-SYNC screen, make sure your main monitor is selected if you have more than one. Click the check mark next to “Enable G-SYNC, G-SYNC Compatible.” Choose whether to enable it for full screen mode only or both windowed and full screen modes, depending on how you display your games.
Click “Apply” to enable G-SYNC/FreeSync. You’re good to go! Enjoy smoother gameplay in your favorite games. Note that some games may work better or worse, depending on whether you run them in fullscreen or windowed mode (“fullscreen windowed” counts as windowed for this purpose). You can come back and change that setting in the NVIDIA Control Panel if you’re having issues mehr

What experience have you had with HDR1000? Are there any other drawbacks you noticed compared to G-Sync?

What graphic card do you have to fully use it at 5120x1440 at 120Hz?? Thank you in advance!