During a spare hour, with my collection out, I thought I would do a test to see which watch had the loudest beep and alarm.
Here are the results of my not very scientific survey.
There was not much difference between the 6900 and the 5600E. The Spike Lee and the 5600C were quieter than the 5600E. My other screwback the GW-5000 just pipped the SL and 5600C. Quietest of all is the GW-M5600, which I assume has something to do with it having the smallest case.