Wow, sounds cool. My first, old HDR TV was only 350 nits and I used to be impressed with that. You wouldn't wanna go blind in the headset either. Man, I'd really like to invest in this thing once I get a ps5. I hope people support the damn thing so the software doesn't dry up, seen a 200 price cut a few days ago, fingers crossed this will help it, it's such cool tech to have it die. 

Neither is particularly important - that's why they are still optional features even after 10 years of being available.

HDR is useful if you have a dim or bright room. 4k is nice if you have a very big display.

I more interesting question would be: how much would you pay for each in a TV set? $50 for HDR , $200 for 4k for me...

According to Reddit sales have picked up a lot. Lot of new posters asking for game recommendations etc.
https://www.reddit.com/r/PSVR/new/

HDR in PSVR2 is already so effective I had to shield my eyes from the windows, lightning outside, as not to ruin my night vision to be able to see detail in the dark corridors. The brightness range is already very cool in the headset.

No worries about going blind (yet)

The ambient brightness of a sunny day with clear blue skies is between 7000-10,000 nits (between 3000-7000 nits for overcast skies and indirect sunlight).
A bright sunny day can have specular highlights that reach over 100,000 nits. Direct sunlight is around 1,600,000,000 nits.
10,000 nits is also the typical brightness of a fluorescent tube - bright, but not painful to look at.

Nah, HDR is now cemented. Every big game releases with it and they at least try for 4k. People are upgrading along with the consoles, so by end of gen 4k will be secured as the standard if you don't already count it as such. 

I've played some games where the brightness peaks like abfade to white screen or an explosion/fire effect and went "whoah, too bright", I suppose mostly in the evening or night. I don't think going past 500 would be a good idea in the headset but sure I've yet to see what 250 in it looks like. 

Umm I've yet to see each feature in a seperate matter to really to see the appeal of the difference but if I had to guess, HDR would most likely feel more important to me because I don't have a problem with Full HD resolution anyway.

Well... I went to Amazon, and while HDR comes with most TV sets, it's certainly not on the cheapest.  So it's clearly not standard yet...

Maybe so, but on consoles and for games releasing it's standard. 1080p was standard for years but you could still buy 720p TV's and you still can I believe.  

I have pretty much no experience with either, but considering how little I care about resolution, HDR would have to be a terrible disappointment for it to not be the right choice for me.

HDR.

4K isn't really necessary in my opinion; most games even on PS5/Xbox Series don't run at 4K natively, and honestly 1080p is fine for me since I sit well back from the TV and my screen's 42 inches.