Stuck in boot loop after flashing superSU (Marshmallow)

Hi all, I am playing around with an HTC m8 to decide if I should use it as replacement of my Nexus 4 (so far, too big and heavy ;)).

But well, I unlocked the phone and installed TWRP. All worked fine, but then I flashed supersu and I'm stucked in a boot loop. I am reading a lot of things but I am unsure about what to do now and how to actually root the phone and start installing a different ROM as I don't know what´s the phone model. It says M8_UL in fastboot...

I´m looking at this but not sure if this phone is gpe.
http://forum.xda-developers.com/htc-...persu-t3242210

Any ideas?

Thanks!