Earlier quoted context omitted.
Cable(s) out to an external drive holder with an ATX -> Sata uplift from a DC psu. I run the radxa USB3->SATA bridge pi-Hat which is a jmicron chipset and with the vagueries of USB- attached drives, but SATA like speed through a serialising controller I do pretty well. I'd like to do astonishingly well. So the use case is "yea I can't fit it inside the NUC case but I can bridge it to a small box" -or run the NUC with…
So, since the form factor isn't the goal here (separate box with umbilical cord, after all), what exactly is the purpose in using a NUC or similarly sized small computer? None of this is intended to be condescending or anything, I'm just sincerely curious about the train of logic here. What you're talking about so far seems like something that would be satisfied by a custom Mini-ITX build with appropriate case/tower…
I've used NUC and they are remarkably well made but you're on the money: they just may not be a good "fit"