I dont think there will be much in it as the 535d will need to be producing at least the same amount of power as the 525d to keep up and may even need to produce a tad more due to the extra weight.

 

The 535 has twin turbo's and thus is likely to suck more juice IMHO at least.

 

If a 525d and 535d were driven areoud a track you would have to go well in excess of 100mph, as the 525d would still be at cruising speed. So this wouldn't be relevant on normal motorways. By the way I like the M3 / Prius clip, I had heard about it, but never seen the clip before

 

And what about those who claim the fuel economy in their 535d is better after getting the car chipped? Power=fuel doesn't add up on that account for me.

cheers

 

Real world figures from spritmonitor.de for:
525d: 8.13 l/100km
530d: 8.33 l/100km
535d: 9.43 l/100km

 

Really depends on how your driving it tbh, if your gunning it then sure, the more power the more fuel your gonna use, my 320d was remapped from the standard 136bhp which was gutless to around 165bhp, my economy overall dropped a little on the average but on a run was virtually no different to stock but with tons of power in reserve when you needed it.

@ Mikael:

Those figures in my experience for a 530d are pretty much spot on IMHO, nice linky thanks