Whoever thought of the awful caconym ‘post rock’ as applied to bands like Mogwai, Sigur Ros and Godspeed You! Black Emperor should be beaten severely and then made to listen to recordings by Pink Floyd (such as the live side of the Ummagumma album), Faust and many such bands in the 70s that produced music at list strikingly similar to what is currently called post rock. It’s not post anything!
On the up side, as badly named as the genre is, it is producing some brilliant music. All of the above bands are quite excellent and their music is also hauntingly beautiful, as well as often being very highly orchestrated and demonstrating technical subtlety not often seen in current rock music. Very good to listen to but also very rewarding to relisten to in order to properly understand the construction of the music.
To call your music post-anything is to admit it’s purely fad driven. Post-punk came after the punk hype died down. Punk was still around, and it was a lot better than the crud that most are aware of (Note: Sex Pistols were a manufactured boy band formed to model a fashion designer’s gear)
Don’t know any of those bands you listed, but if they’re playing music like Floyd they’re rock. Just rock – that is, if you need to apply a label :)