I just received the XG27AQM today from amazon.
For my FPS/Competitive games: (I tried Valorant, Apex, COD: BO, and SC2)
ELMB/strobing is overall great in motion blur reduction with the con of lowering the brightness (I was spoiled by dyac+ when I had the xl2646k but returned it because of TN color and 1080p not 1440p).
The ELMB's brightness reduction was low for me at first but I got adapted to it when I played without my window blinds open. Using the shadow boost also helps here for certain games which are too dark with the ELMB dimming.
The OC works great and I get 270 Hz without any problems.
I did not notice any flickering that some users have reported and I can run the panel at 10-bit color with Nvidia control panel.
For single player games: (I tried: Red Dead 2, Witcher 3, and Control)
G-sync compatible works fine here and I changed the OD to 3 to get the biggest range for VRR without getting too much overshoot (around 120-270hz).
For ELMB-sync (G-sync + ELMB) you initially get locked out of the OD settings. However, you can bypass this lock with the service menu (unfortunately the OD needs to be reinput into the service menu every time you restart your monitor). Please check liquidshadowfox's detailed guide on this thread (he gives also a detailed list of what OD settings to use dependent on how many Hz you get from VRR matching with what frames you get):
viewtopic.php?f=2&t=8826&start=50
Other:
The sRGB mode initially locks you out of changing the brightness. A XG27AQM owner told me you can change the brightness while sRGB is enabled via the service menu which saves after you input your desired brightness. This fix has solved that issue for me.
The colors of the monitor are wide gamut which is fine for me as I came from an LG 27GL850-B. (felt like I didn't even change monitors color-wise)
My unit came with your typical IPS glow and no dead pixels.
Concluding thoughts:
I will be keeping the XG27AQM as my main monitor and have cancelled my pre-order for the PG279QM.
I feel the XG27AQM provides a high refresh rate (270 Hz OCed) with great motion blur handling and with the 1440p for my needs of competitive FPS gaming and mixture of single player games. Not mention it is also 200 USD cheaper!
I have not tried the PG279QM yet but I feel missing ELMB/strobing will be more of a feature loss for me than the g-sync module's dynamic overdrive which I myself can tune with the OD menu and the service menu (if I have ELMB enabled with g-sync aka ELMB-sync).
Overall, if you just want out of the best monitor experience without the need to tweak settings go for the PG but if you are more of an FPS competitive player (270hz + ELMB) who also loves single player games that do not mind setting tweaks go for the XG.
I hope this helps anyone in the same predicament.