From that era, the diesel is likely to be the same straight six fitted to Omegas (though might be the common rail variant?). I've driven one, and it truly was "sedate" and the throttle was simply a volume control. However, I quite liked it. In fact I really liked it.
I've also driven some of the V8s, including the notoriously incontinent BMW 4.4, and the Jag ones in both NA and Supercharged. The NA go quite well in a refined "this doesn't feel that quick, oh shit I'm doing 100mph" type of acceleration way. The supercharged does go well, but the one I drove I found myself thrashing everywhere - something I didn't find I was even attempting with the straight six diesel.
At the price I'm guessing you're looking at, you may get a petrol facelifted L322 for the price of an early diesel.
Even if you have the right contacts for cheap parts and repairs, they will always be an expensive car to run, both fuel wise and things like tyres.
joshwyatt is your man to talk you through L322 RR's