Snapdragon has excellent single-thread performance (unlike Ampere) if that’s what you’re asking.

Qualcomm are slowly but steadily improving Linux support for the X1/X2 Snapdragon CPUs (such as the qcom-hamoa-ec driver in 7.2), so it's still a wait. I think there's some challenges with Secure Boot and the firmware with these Lenovo devices though.

Unlikely. I've been daily-driving the predecessor (X13s). While it's usable and technically all drivers are there, it's far from "without pain" due to endless number of small but annoying quirks. Just to give you an idea: boot fails 4 out of 5 times, external displays aren't recognized unless plugged in/out several times, sporadic resets during overnight sleep, etc. On top of that speakers will sound prohibitively tinny due unimplemented software-side speaker protection. I haven't tried T14s, but at least the audio issues will still apply there.

Apple devices supported by Asahi are a far more polished experience.

When I looked at this before I found https://github.com/kuruczgy/x1e-nixos-config - reasonable though not 100% support.

I believe Ubuntu also has semi official X1 elite support, no idea if they're working on the latest generation.

No. The driver support is very poor and won't run at all well.

Even. Setting it up is a pain: https://github.com/Jeremiah-Hawley/Linux-on-Snapdragon

It can run Windows well though.

Without pain? I mean, there is pain when using Linux. It just works better than, say, Windows.