I've been talking to an old racer friend of ours - Mark Hill @ MHP Exhausts. ( https://www.facebook.com/racesilencers/ )
He's a wealth of knowledge and a real good fabricator. He can repair / repack / quieten down most types of exhaust - usually without serious losses of power. Mark's worked at all levels and has built ''quiet'' systems for several BSB teams.
From experiance the normal problems we have are : old V twins with silencer packing ''shot'', any sort of short / stubby / Moto GP type silencer ( especially 600's ) and 750 / 1000's with basically unsilenced pipes. We've now found the cheap, Mickey Mouse DB killers are useless and block the exhaust system full stop.
If you fit any sort of DB killer it MUST be ''bolted'' in and NOT lock wired - they fall out ! Having one ''shot out'' at over 50mph ain't fun...
From Mark :
''My 400mm sleeved can is 101db static new, 94 drive by at Snetterton, on your average 600/1000cc in line 4.
450mm sleeve will be 99db, and never had an issue on drive by.
Yoshi gsxr 1000 will just need a 60mm dia bend of 18 degrees, I made a few up for Hawk Racing at the start of the year so they could test their Superbikes at Mallory Park. Then you can slip on a normal race silencer.
I can do a Hex mesh that reduces drive by noise with little effect to power.
I have made various baffles for the Ducati's, Akra V4, and some V twin 899 and 1199 types.
Anyway it's January now so you've plenty of time to get any queries sorted before the season kick off in March !
Hope this helps