So This morning after like 20 hours of assembly my bike was at least rideable and I took it to work.
I made a custom 6sp cassette out of 2 hg60 8sp cassettes (no carriers at all in these). I made a 13-30 cassette (42 up front). I all looked good and I put the rd on there. eyeballed the limit screws, pulled the cable tight and bolted it down.

The first ride with the bike was when i was going to work, and i was 1,5h late, never ridden there but knew the general direction I hadn't even tried shifting it through the cassette and figuered I would adjust it on my way to work so i brought my wrenches.

And to my surprise it shifted perfectly, didn't have to adjust ANYTHING shifter/rd related, no weird sounds, no nothing, didn't even touch the barrel adjusters. Just perfect shifting. Thats what I like about 8sp. its so insensitive its like magic.

Only downside was that the biggest cog was too far outwards so it didn't want to shift up to it. essentially I had a 5sp. I fixed it later though with the tension screw, but still i want to move the cassette inwards a bit. And I made spacers at work to make that happen.

Oh and the joy of not having to double shift every single time you shift, priceless.

With my old 9sp, doing this would have derailed my chain and probably ruined something expensive, I don't even wanna know how 10sp and 11 are, and i never will, because they are like the pinnacle of useless POS engineering ever pushed onto market.

I eyeballed it.... and that was the only "adjustment", and then it just worked, seriously. I'm really happy. The good old days are back. when you adjust once and never touch it again.