I just had a professional rigger who has done lots of traditional rigging answer my question regarding 7x19--but not through this board. For anyone searching for the same info, the answer I got was to pre-stretch the 7x19 (method was described that I'm sure all you professional riggers here already know about) expect about 2" of stretch. After the pre-stretch, don't worry about using 7x19 or 6x19 IWRC but don't ever use fiber core for this app. If concerned, go to the 7/16" on the galvi for the longest shrouds and backstay but stick with the 3/8" galvi for the rest.
Best to all
