I would be more concerned about crossing the lines until each line has been breed to remove defects. I am not crossing any of my lines at this time because I don't want to have to deal with a whole new set of recessive traits popping up.Apart from T-M who are they? I would really really like to know!!
Like I said, until serious breeders are selling their improved stock (improvement takes time/years and more than one or 2 crosses between 2 lines), and those breeders become well known as reliable it is difficult to know for certain what you may be buying. I hear complains about how people are buying birds from "reputable breeders" for good money and they are not worth keeping/breeding. Most people on this thread are relatively new to cemanis and are still improving their stock before they are good enough to sell - or at least that is what they SAY they intend to do. I am not sure how long you have been breeding them. At least with Greenfire AT THIS TIME you know what you are getting. They are not perfect but not horrible either.
Also GFF are VERY careful to be sure the customer is happy with what they have bought. So far I have not heard a single complaint about a GFF cemani.
Of course I am also only willing to sell my improved stock only to other experienced breeders at this time as I am more concerned with an inexperienced breeder claiming my name and selling culls to make a quick buck. In fact, I may not even sell any Cemani this year and will probably just focus on Svart Hona.