Well, I have to confess that I'm not attracted by Diesel engines, not even by high power ones.
I have a friend who wanted to buy a new Mercedes ML 400 CDI a few weeks ago. He owned a Mitsubishi Pajero TD before and wanted to have something more powerful for his family.
We met at his Mercedes dealer and he testdrove the ML 400 CDI. After the testdrive, he was sure that he wants this car.
He was always laughing about me because I bought a ML 55 AMG and he thought that this is SUV overkill and doesn't make sense. His dealer told him that he'd have to wait around 8 months for the ML 400 CDI, so the dealer convinced him to testdrive a ML 500 (in stock) too. After the testdrive, he was even more impressed and bought the ML 500 instantly.
The high power Diesel engines are nice but they're not sporty. They provide a lot of torque but they usually have a lag when starting from standstill. I testdrove the ML 400 CDI too and I didn't like it. Whoever spends so much money on a Diesel must be crazy. Saving money? Maybe. Environmental reasons? No need to buy a SUV.
My personal conclusion: people who buy a high power Diesel usually want to prove themselves that they save money. Doesn't make much sense to me. If I have the money to buy a ML 400 CDI, I'd have the money to buy the fuel for a ML 500 too. And the ML 500 is definetely more fun.
The new VW Touareg V10 Diesel engine is interesting from another point of view: it's standard power of 303 HP can be easily raised to 350 or even 400 HP due to the bi-turbo technology. This would be another thing I don't understand: a lot of ML 400 CDI buyers tune their cars to 300 HP and more (simply done with a ECU software mod and other minor mods).
So why not buying a ML 55 AMG instead?!