Have you tried the Neo80 keyboard yet? That is an interesting budget board. [It's not 'budget' quality.]
That is the only one in your list that I have experience with. I also have a KBD8X MKII. What I can say is that I don't see how the MKIII stands out in today's market, but it is probably a 'solid' board.
I just got NK Classic TKL keybaord kit - looks really solid, good quality. I need to build it, hopefully in next few days.
I have a Classic TKL - typing on it right now.
It's a solid board, but I find the typing experience a little harsh. Like maybe the plate doesn't flex like it should. But I'd be curious to see how it goes with you. It could be that the Hyperglide Browns I am using with this build are snappier than pre-tooled.
I'm slowly leaning towards throwing all my keyboards through the window...
I've been trying to build that Classic TKL last night - having problems with stabilisers. They are very sluggish, I did not over lube them. I played with differnet caps, had pbt caps swim in boiling water (pbt PBS set) to try and bend them a bit, cause noticed that cap stems were kinda not aligning with stab stems. Got that right, then had to bend stab wires a bit, cause it looked like those were pushing stabs sliders to the edge of it and scratching on those walls too heavily.
Then after 2 hours of trying things I got it right - they worked fine - but then I realised that there is something wrong with actual build - stabs felt ok when straight on pcb, but as soon as I put on plate, they started to get stuck! WTF!!!!!!
That Classic TKL has screws for pcb+plate, so I took those out, moved plate around to see when it stop "blocking" stabs, there are moments were it works for one stab, but not for all... How the hell plate can have impact on stabs? I think only moment would be when moved to one side, it moves actual switch away from the center of stab and somehow make it all sluggish/stuck.
That's two different sets of stabs (TX AP Screw-in and clip-in), different caps (pbt PBS set, SA, HSA, GMK), switches... I'm on the edge to give up

Or sell it all and buy pre-built keeb, maybe I'm too old and this **** is not for me anymore...