The X220 was for many long-time ThinkPad users the last good one. It had real keycaps and no trackpad. Too bad about the display, since the X220 was during the era that Lenovo was gaslighting buyers about how IPS panels simply could not be procured on the open market, right before Apple showed them to be liars. The X220 display is truly ghastly.
Like some other X-series enthusiasts I consider the X61 Tablet with the AFFS panel to have been the pinnacle of the series.
The X230 is nearly identical physically, and you can swap the X220 keyboard onto it.
Advantage being 3rd-gen/HD4000 igpu which is Vulkan capable, not available on the X220. This difference makes the X230 far more practical in terms of modern graphics development/environments.
Pretty sure it's just a matter of getting X220 palmrest/plastic trim surround to avoid any alterations. You can find writeups via the obvious searches, here's some such results:
Also after the X230, the next few generations of intel CPUs that thinkpads used really focused on low power over performance. So because of that it performs like much younger laptops.
Like some other X-series enthusiasts I consider the X61 Tablet with the AFFS panel to have been the pinnacle of the series.