If you want to use ConsoleHDR mode and the tool then I'd set both to 1000nits. Just know that ConsoleHDR mode doesn't track PQ well past 300ish nits to reach 1000. It'll still do 1000nits, just not tracking PQ. It's probably not a huge issue since we're talking about specular highlights in games, but it's worth mentioning. I'll add this info to my initial reply.
Personally, I only use HDR in HDR supported games and don't use AutoHDR, so I just ignore the Windows HDR Calibration app since peak brightness can be set in most games I've come across. If you use AutoHDR, games that don't allow for peak brightness adjustment, or the saturation adjustment feature of the Windows tool, then just set it to 1000nits on both screens in ConsoleHDR mode.
This info is only for gaming. If you watch HDR content on the monitor I would use one of the tonemapped modes, probably CinemaHDR since it should be the only mode that properly adapts its tone curve to maximum display luminance metadata 4000nits. I need to measure this to confirm, but it's how it works on some other Asus OLEDs.
That reminds me. During one of my conversations with Asus, they mentioned that Brightness should be default 90, which is the case for their new ultrawide WOLED, but as we all know the default for this monitor is 100. I never bothered to measure at 90, perhaps it will result in a 2% Window in ConsoleHDR mode tracking PQ correctly. I have noticed that HDR movies in ConsoleHDR mode sometimes have posterization on skin, which is also the case with the new ultrawide when set to 100. I'll measure later today and update this thread if it shows any differences worth mentioning.
EDIT: I tested adjusting brightness and it doesn't have any impact on ConsoleHDR PQ tracking, just lowers output brightness. I also tested GamingHDR and CinemaHDR to check out they adapt their tone curves for movie content. CinemaHDR is the only mode that properly adapts its tone curve to maxMDL 4000nits.
