Not a silly question at all. Basically, because the power delivery - bags of low and mid-range torque - of a modern diesel are much more akin to those of a supercharged AMG than of the V6, and I like bags of low and mid-range torque. It's taken me a while, and driving the Pug, to realise that that's what I want, what I really really want... (that's a good line; somebody should set it to music).
I have to admit that I enjoy driving the Pug - 147 hp - more than the E350 - 306 hp - simply because of the torque characteristics; they suit my (relaxed/laid-back/lazy - sh1t! I really HAVE grown up. Where did I put my pork pie hat, pipe and slippers?) style of driving much better. I'd prefer an automatic, though, and an E320 will be an automatic.
An E320 CDI should be like the Pug on steroids, and even better if/when I have it remapped...