"Anyone care to write out what to do at the various testing companies and GEDMatch to compare X results"
I can explain how it worked for me on 23 and me.
In the DNA relatives section is a long list of people with whom you share more than 7cM of DNA. You may be able to contact the individuals who you share with . I was contacted by a man from Canada, I didn't recognise any of the names on his list of surnames and it wasn't a large match so it wasn't one of my priorities but I said yes. In a section called Family inheritance advanced I was able to compare his genome to mine and discovered that the match was a segment of 26cM on the X chromosome This person also had a family tree on My Heritage. Looking at that, I did recognise a name, Lucy Satchell meant nothing but fortunately he had included her maiden name of Gurney,which did.. I knew that my gggg grandmother was married to a Gurney..
It didn't take much research to find that Lucy's father Jeremiah Gurney was the brother of Arthur Gurney, my ggggrand father. They had the same mother. The x chromosome pattern was correct (ie there can't be two male descendants in a row because a man receives his x chromosome from his mother)
In the 'widget'
my Canadian 'match descends from Bessie Lainchbury
He actually has a guest member profile on wikitree but has not confirmed it, so I don't feel able join the dots on here.
There's a really interesting article on the X chromosome here which also throws some light on how Family Tree DNA reports matches (it seems that as this match was just on the X chromosome it wouldn't have been reported! ) https://dna-explained.com/2014/01/23/that-unruly-x-chromosome-that-is/