Thanks a Ton Paul!
Yes, the equal one is exactly the same what I was looking for.

I tested the code for a data with 100,000 rows and 25 columns, your equal code got completed in 1 minute and 13 seconds.
but my simple random sampling code made excel stuck and completed in 13 minutes and 20 seconds. Request if you can look at this whenever you get time.
There was a mistake in my code in loading the column headers
colStrataPicked = WorksheetFunction.Match(combx_Fields.Value, .Range(.Cells(1, 1), .Cells(1, colLast)), 0) ' it was rowLast by mistake
Once again, many thanks for your time and help Paul