Who would have expected a Diesel to win Le Mans last year?

This is apples against oranges.

The E39 M5 is now 10+years old in design terms, whereas the new BM diesels are cutting edge.

In dimishing returns i would expect their top of the range diesel to be damn quick (maybe not quiet as quick as the E39 M... but there we are)

Put your diesel up against an E90 M5...this would be apples against apples... i think even wth your remap it would be a different story.

To concur with JJ; throw your motor down some twisty stuff and the lack of LSD will be its achillies. I also wonder whether 'mother' will smother all the power round bends?