So, tried some more.
Was watching some nature videos. 
from czechvr.com via VirtualDesktop
First was watching 4k content (i had already downloaded a year ago) and that looks amazing already.
Then i downloaded new 8k content. Was even better, more detailed. But even with lower quality you have a weird feeling of presence - what it´s all about - isn´t it? 
Then i tried HiRes youtube videos via VirtualDesktop. size 90deg, 1.5m distance. Distance similar to a movie theatre. Desktop was at 1440p and stream, too. Already that was amazing. Did not try real 4k - can only be even better. First time you think you look at a normal Monitor, not focusing on sde.
Then i thought i could use this setting to compare my index and switched to it. Well, i almost forgot how i immediately focus on the sde while watching movies with the index. If you slightly move your head while watching it looks great because the sde gets kind of blurred. But as soon as your head keeps steady, the picture becomes sharp and the sde jumps right into your eye…
Nevertheless compared the sweetspot aaaaannnnndddd: felt better (reasoning below). The numers at the bottom (timeline) and the Title on top/left was less blurred than with my 8kX. saw no barrel distortion when looking at the borders of the movie “wall” but slight warping inside it. roughly at the point of half of max fov of the index there was some slight warping going on. And also on top. On top was also compression going on.
Then i started HL Alyx with the index. Steamvrss resolution was around 2300v pixels. Went to the balcony and enjoyed the view. I did want to compare the fov and warping/clarity with my 8kx. so i went around one meter left of the radio on the table, looking straight ahead to the citadel. down, outside of the balcony you see two leafs. i centered myself on the right leaf and checked how far i could see from side to side and up and down. with the index i could see up to the massive high block on the citadel and below i could almost see the balcony handrail. Left i could see until (including) the round windows like structure of the combine outpost and right i could see until (including) the big rooftop window of the next building.
I focused on the smoke coming out of the cimneys and was suprised about the details i saw there. BUT the screendoor when my head was still. terrible. was the same impression as before when watching videos.
Clarity/sharpness is simply so much better on the 8kX.
Then i checked the blur area of the lenses again. Was pleased with the amount of blur. Better than 8kX (reasoning coming soon). Then i switched to the 8kX again.
First of all i switched pp on and dialed steamvrss to 100% (3004v pixels, FOV small) compared back with pp off and have to say that it is overall a better experience with pp on (contrary to my old thinking).
Checked the details and have to say it is a massive improvement in clarity over the index. checked the fov and could see now (from the same position as before) another roughly two centimeter in the lenses further. left to the end of the combine outpost and more, right to the end of the rooftop around the corner of this building and below i could see the handrail. but i couldn´t see as far up as before - minimal less far. Reason for it could be my vertical ipd offset of -2 on both eyes. But i am not sure about that.
Checked the blur of the lenses (sweetspot) and was positively and negatively suprised at the same time. It looks to me as if the blur of the index lenses is starting earlier but is less intense. So i think the sweetspot of the pimax lenses is overall bigge, but sharpness degrades quicker over fov.
So my feeling about the better clarity of the index was not completely wrong. But after having swapped the index with the 8kX, the improvement in quality is so big that i never want to go back (exeption: 144Hz needed)
Can not test more today, will do next week.