On the older models you can also do a mod to sacrifice your DP port for use internally with an eDP panel. There's one for the X220 to do that. Although if you're okay with 1366x768, the X220 Tablet models all have IPS panels from the factory and don't look too bad.
The X220/X230 mod uses the docking port's DisplayPort lanes, instead of the DisplayPort port. I'm still able to use the DisplayPort port on the X220.
The T420/T430 converter doesn't use DisplayPort, but simply converts LVDS to eDP.
I used the B140HAN01.3 (AUO panel) for my T420, which my friend also got for a T440p. Colors and viewing angles are great on it, likely the Razer Blade panel you mentioned.
The X220 mod was a pain to install IMO - soldering to tiny solder points on the motherboard, soldering the sense wire which needed burning off the enamel from the enameled wire, and having to cut out (I used flush cutters) parts of the top case for the new display to fit. My first install wasn't great either, with a cold joint causing issues I solved later on by reflowing the joints.
The AUO 14" panel has better color gamut (IIRC 100% sRGB coverage) than the available 12.5" panels for the mod.
