I daily a T480 with Debian for work, and I'd recommend it highly. Great performance, battery, build quality, look & feel, etc. We have some 7480s deployed and while they've been solid as well, I much prefer the thinkpad. T series will have better performance and battery than X series, also, so I'd take the T480 over the X1C.
how is the build quality of the t480? I had a t580 for work, and that one crashed when you picked it up at thr wrong corner. and after a month over the warranty, it completely died
boot into the bios config menu to make sure it's unlocked (if it's locked and they don't have the password that'd be a dealbreaker for me)
boot into a live linux environment from usb and test both batteries, keyboard, trackpoint/trackpad, speakers, microphone, wifi, and all external ports (T480 has 2 usb-c, 2 usb-a, ethernet, hdmi, headset, and sd - make sure batteries charge well from both usb-c ports)
to check the storage health, install nvme-cli if not installed, run nvme smart-log /dev/nvme0 and check the "percentage_used" value: if it's near 100% it might die and need replacement soon
to check that the vents, airflow, and cooling hardware are in good shape, install stress if not installed, run stress -c 7 to load up 7 of the 8 available cpu threads, make sure the fan spins up good and strong, and watch /sys/class/thermal/thermal_zone0/temp to make sure the cpu temperature stays under ~90-95 degrees
On my own time later, I'd run memtest86+ overnight from bootable usb to check the memory, then install tlp and run tlp recalibrate with the laptop on the charger to recalibrate the batteries
Edit: enjoy the new laptop! I hope it works great for you
I've actually managed to find a used Carbon X1 Gen 6 (i5-8250U, 16GB, 512) for 310usd so I reordered that instead. I assume the course of action won't really change in this case.
And I'm not too familiar with some of that stuff, do you mind if I ask you the following:
Where can I see if Bios is locked?
Best way to boot into a Linux environment with a USB? Where can I get a Linux distribution that would work seamlessly from a thumb drive?
Is there a testing app for the microphone (it's important for me) and the ports?
And what's the fastest way to see the battery health?
How to install 'stress'? And how can I watch "/sys/class/thermal/thermal_zone0/temp"?
Sorry, all of the linux stuff is just specific to my own preferences/environment - if you're more familiar with windows it would be best to just use that for testing. Presumably it will come with windows installed?
If so, put some programs on a normal usb storage device and then install/run them from there.
To test the microphone/camera, I'd just use whichever app you'll normally be using them for
As for the rest:
When you first turn the laptop on, at the red Lenovo splash screen, press Enter repeatedly to get into the boot menu. Once there, it'll give you a list of options with associated keys to access them - go to "BIOS Setup - F10" (or something similar, not sure of the specifics on the X1C 6th gen). If it prompts you for a password to enter that, it's locked.
To test all the ports, plug your usb stick with the apps on it into each of the usb ports and make sure it shows up in explorer; try the same with an sd card if you have one; plug in to a wired ethernet connection and make sure you have internet access through it (disable wifi at the same time to make sure); plug headphones into the jack and make sure they work; plug into an hdmi display if you have one.
To check battery health, run Command Prompt with administrator privileges, then run powercfg /batteryreport to generate a battery health report