I have all three headsets at this point (Oculus Go, Quest 2, Pico 4), so i think i can give you a pretty good advice. YMMV though
The Oculus Go was my first headset and apart from the overheating issue and the bit small FOV its still a good device for JAV. SDE is definitely more visible then on the other (newer) devices. What made me upgrade was mainly the overheating, as i couldnt watch more then 30minutes without overheating which became pretty annoying. Also at this point as the headset is discontinued players wont get any updates and Heresphere is obviously not working.
I upgraded to the Quest 2 as soon as it got released in September 2020 and is has been my daily driver since then. Being able to stream standalone without any overheating issues is a big plus, also Heresphere is available as a standalone app. Imho Heresphere does improve overall viewing experience as it has autofocus integrated and other features to correct scaling issues. Also the option to connect it with XBVR and create your own JAV VR "Netflix" with browsable movies (by thumbnails, categories, tags) is pretty nice. Talking about the quest 2 itself, it suprises me to hear that the Quest2 supposed to be uncomfortable. With that VR Cover padding its pretty comfortable much better than the Pico 4.
I ordered the Pico 4 some weeks ago as i was curios about the pancake lenses and overall performance. Good thing is that the front is not as bulky as it is on both Oculus Headsets, thanks to the pancakes. Also the lenses have a very good Edge2Edge clarity. To have a stepless IPD adjustment is also nice although i am fine with my IPD on the Quest2 as well (i got 64mm). Unfortunately there are some downsides to this headset why i am returning mine and would not recommend it:
-lenses: while clear and having a big sweetspot, there is something called lensflare by some reviewers. It somehow looks like the lenses are dirty and tbh its bothing me quite a bit.
-comfortability+padding(light leaking): At least at this moment the padding is pretty uncomfortable compared with the Quest2 and more importantly at least on my face it leaks a lot of light in the lower part. That basically means you still see your room if you look down. Something i never experienced on the Quest 2 /Go and obviously bad for immersion. Maybe this will be improved once VR Cover will produce something but at this moment they dont.
-software/player options: might sound trivial, but at this moment there isnt any VR player besides the built in player. The player itself allows to play via network and does an OK job. DeoVR is supposed to be released, but at this moment its not available. As Heresphere is developed by an US guy, it wont be released on the Pico headset soon. Thats quite a pity as this player does improve the overall experience a lot. As the headset doesnt have a DP, you can stream only wireless (the original streaming software is supposed to be terrible, but Virtual Desktop should work pretty good) which does have some compression.
-refresh rate: this is probably the most important reason. The Pico 4 only have a refresh rate of 72 or 90hz. To have videos player without any stuttering you want to have a refresh rate that matches the frames per second of the video or having a multiply of that. The Oculus Go has a refresh rate of 60hz so it perfectly matches the 60fps videos. Quest 2 also supports 120hz so its a multiply of 60 and still stutterfree. Unfortunately with Picos 90hz you will always have some kind of microstutters. I am not sure if a software update could increase the refresh rate to 120hz, but at this point they dont.
verdict:
JAV VR that is currently released is in 4k and you wont have a massively better experience to be honest. 3 months ago DMM/Fanza released a free 8k video which looked pretty nice but no regular 8k movie has been released or even announced (aside from two 30fps movies with bad quality on afesta). I hope/expect we will see 8k as regular releases at the beginning of 2023.
The Quest 2 is still a good headset and i would recommend it, although given its already two years old and price was even increased, i would rather wait for the Quest3 (which was confirmed by Mark Zuckerberg to be released in 2023). Especially given the fact that there is no 8k JAV at this moment.
Pico4 is rather disappointing to me (lensflare, software, light leak, refresh rate) so i wont recommend it. Luckily amazon in my country has a very generous return policy. So maybe thats an option for you to order a Quest2 and/or Pico4 and check it out for yourself.
To keep it short: my advice would be to wait for 8k releases and upgrade then potentially to the Quest 3
