Of the three, the ROG SWIFT PG279Q / Asus ROG Strix XG27UQ outclasses most other IPS SCreens like Secretariat in the Belmont Stakes (32 lengths). 1st clue is the panel ... AU Optonics is the Gold Standard.
As far as response times go ... every spec sheet and advertisement you have ever read is BS. Asus advertises 4 ms for the PG279Q which is excellent. But it's not real. Here's the tested results:
Minimum Response Time: 4.10
Average Response Time: 5.0
Maximum Response Time: 6.5
Asus exaggerates just a bit using minimum response time instead of average and dropping the 0.1 ... Most manufacturers are worse. I have see advertised 1.0 test out worse hen the Asus "in real life'
Here's a comparison of response and lag times
Now lets look how bad it gets with some of the less reputable brands ...
AOC advertises the AGON AG352UCG at 4ms .... 4 ms my ass.
Minimum Response Time: 3.3
Average Response Time: 10.2
Maximum Response Time: 48.0
As good as the above Asus monitors are, I prefer the Acer XB271HU bmiprz for one big reason .... At release, both Asus and Acer used the same panel from AU Optonics ... about 18 months in, Asus switched to an 8-bit panel while Acer maintains the 10 bit panel.
If it can't do 120 Hz w/ G-Sync turned off / ULMB on, I don't consider it a gaming monitor. 4k, 60 Hz monitors don't make the cut and 144 hz don't have ULMB. I find most gamers prefer to turn G-Sync off and ULMB on when maintaining fps > 75 or so.
A detailed look at variable refresh rates (VRR) including NVIDIA G-sync, AMD FreeSync and all the various versions and certifications that exist
www.tftcentral.co.uk
It should be noted that the real benefits of G-sync really come into play when viewing lower frame rate content, around 45 - 60fps typically delivers the best results compared with Vsync on/off. At consistently higher frame rates as you get nearer to 144 fps the benefits of G-sync are not as great, but still apparent. There will be a gradual transition period for each user where the benefits of using G-sync decrease, and it may instead be better to use the ULMB feature if it's been included, which is not available when using G-sync. Higher end gaming machines might be able to push out higher frame rates more consistently and so you might find less benefit in using G-sync. The ULMB could then help in another very important area, helping to reduce the perceived motion blur caused by LCD displays. It's nice to have both G-sync and ULMB available to choose from certainly on these G-sync enabled displays. Soon after launch NVIDIA added the option to choose how frequencies outside of the supported range are handled. Previously it would revert to Vsync on behaviour, but the user now has the choice for various settings including Fast Sync, V-sync, no synchronisation and allowing the application to decide.
If ya got the juice in ya GFX card and can maintain 80, 100, 120 fps ... you will at least want the option of having ULMB available. I been waiting for it to show up at 4k before i could justify walking away from the Acer. Frankly, the appearance on the Asus monitors w/ AU Optonics panels looks sturdier .... but I prefer the 10 bit image on the Acer ... not to mention, the 4100 price savings
pcpartpicker.com
so in answer to your question ...
"If you had no budget restrictions, which 27 inch gaming monitor would you choose for the mentioned specs (I9-9900K + RTX 2080 Super)? "
I'd buy the $595 Acer XB271HU bmiprz
To narrow ya search, I almost wanna say, if it ain't here, don't bother looking at it
But that would be unfair as when say they review the Asus ROG Swift PG278Q, they'll likely skip the Asus ROG Swift PG278QR ... and when they review the Acer Predator XB270HU (144 Hz), they skipped the Acer Predator XB271HU. But if it's not "just released" and they didn't bother to review it, minor upgrades aside, it's pretty good bet, it's not worth having.
