Linux distros I have tried include: ubuntus, debians, fedoras, opensuse, manjaro, endeavour, mint. No slackware, redhat, centos, gentoo, nix, kali, steam.

Good. Some light weight suggestions for your devices to try :

• https://www.crunchbangplusplus.org/
• https://puppylinux-woof-ce.github.io/
• https://www.damnsmalllinux.org/

like netbooks I picked up only because they were cheap

Netbooks as in for example Asus EEE models ? I think some of these models had really slow hard disks and also needed some tweaks for some part of the hardware. The difference in your hardware success / failure is perhaps mainly because of the different kernels and the hardware support of a Linux distribution release (btw, Debian 12 aka Bookworm had for the first time non-free firmware bundled with the installer). In general I think refurbished old Thinkpads should be fine with Linux. Here's two dedicated wikis for that :

• https://wiki.archlinux.org/title/Laptop/Lenovo
• https://www.thinkwiki.org/wiki/ThinkWiki