Diesels aren't as sensitive to backpressure as gas engines. You might get up on boost slightly quicker but your gains will be minimal as the stock exhaust flows quite freely. Others have tried it here and the general concensus is the only real gain is noise. So if you are dying for attention go for it, otherwise save your money.

__________________
green 85 300SD 200K miles "Das Schlepper Frog" With a OM603 TBO360 turbo ( To be intercooled someday )( Kalifornistani emissons )
white 79 300SD 200K'ish miles "Farfegnugen" (RIP - cracked crank)
desert storm primer 63 T-bird "The Undead" (long term hibernation)

http://ecomodder.com/forum/fe-graphs/sig692a.png