Ok, I think I was wrong in my last post, saying that we gonna take our time... last night we went to the next boss in progression... Malygos.
I didn't raid sunday and monday, and monday, XII took down Sapphiron. So last night, next up was Kel'Thuzad. Being the tank with the lowest health, I decided that I would tank him/her, so the other tanks could longer withstand the adds-debuff. Let me tell you, a lot off tanks died :p, and at 3%, no tanks where left... but it was enough. I think it was our third try, so not that hard to learn.
Now Malygos, that's a different story, I think this will take some more wipes, but that's what we do... through wiping, we learn.
By clearing Naxx25, XII is now the 4th Horde Guild on Ghostlands that cleared Naxx25, and I think the 9th serverwide. Not bad.