The Asus Rog Strix XG27UQ is a 4k 144hz monitor. Even a RTX 3080 wouldn't be enough to get 144 fps.
Even if you could get a RTX3080 at the moment you don't have enough money left over for a 4k 60hz G-Sync Monitor.
Even Freesync monitors that have been tested by NVIDIA and deemed G-Sync compatible are either out of stock or upwards of $800 for 4k models.
Freesync monitors are generally a lot cheaper than G-Sync ones but you need an AMD card to support variable refresh rates.
The Ben-Q monitor linked above is really cheap but not good. It has a fixed refresh of 60hz and is a TN monitor. So you either get 60fps, get screen tearing if it dips, fix the fps to 30 if games support it or turn on V-Sync.
I would say that the sweet spot for gaming at the moment is high refresh (144hz) 1440p (QHD) IPS monitors with a low response time. You could buy a decent monitor with money left over. Your existing RTX 2070 Super is a reasonable card for this type of monitor.
When RTX 3070 or even RT3060ti cards become available you could upgrade the card then, perhaps as a birthday present?