I had a Chevy Silverado w/a Duramax diesel...one of my favorite vehicles ever.
With turbo diesels (especially in heavy duty truck form) you can really crank up the boost and fuel and never have to worry about blowing internals or reducing engine life. Stock, they have super high compression and the needed strength to allow them to chug for 300k miles.
My personal experiences were as follows (Granted, it was a HD Truck)
06 Duramax LLZ stock power: 360hp, 650tq
Edge Juice/attitude Programmer
Boost was able to be raised (safely) to 33psi.
With these simple, and rather inexpensive mods, I was able to have 610hp and 900lb/ft tq. A 250hp/250tq increase.
Basically, I think these diesels have a ton of potential that so far underrated. I'd like to see some tuners and even race teams go all out on building a crazy fast 335d.