It has been proven that writing to a file line by line could be faster than building string in a memory.
I would try

lcFileName = "..."
ERASE(lcFileName) 
SCAN 

lcLine = myTable.Field1 + CHR(9) + myTable.Field2 + CHR(9) + CHR(13)

STRTOFILE(lcLine , lcFileName, .T.)

ENDSCAN
cMyString = FILETOSTR(lcFileName)

>I need to add extra formatting text between fields and dependent on field contents. So simple COPY will not work. Do you think using SET TEXTMERGE TO VARIABLE will be faster?
>