I have had my 45mm termis on the 748 measured by 2x different tracks, with what seemed to be the same meter, at about 4,000 (?) and one read 102, the other 98.
Either way I was allowed out - just!
80db is unmanagable on a Duke I'd say with standard pipes.
Get them tested maybe?
Donington and Oulton Park certaintly have the kit.
Best of luck
Tim
ps - try a search such as "db meters" on Google - came up with
http://www.gracey.com/prod-07b.htm [Edited on 3-9-2004 by aws]