Wow, no one ever replied to you eh? Well my guess is you'd b looking at over 100db. The SLP setup with the factory cats puts out something like 102db so without cats, a Mac O/R H with Flows will definitely be more than 15 dbs higher than the limit you posted. Actually, the stock exhaust on a 99-04 stang will probably be close if not higher than that limit.
My Mac O/R H pipe is on the way and once I install it, I expect my ProStreet mufflers to announce my presence 5 blocks away if I get on it hard...but I will plan on keeping my revs lower than 2500 in the city to avoid the popos from giving me sound tickets.
I kept going back and forth between catted or non catted aftermarket mid pipe but the caep cost of the Mac O/R H finally won me over.