While mine isn't reliable yet, it is tuned that bit higher and it will give much faster cars a run for their money. handling wise it will be the same in the derv as the 180 as the KV6 and L are about the same weight, so it would just be learning to drive in the torque band not the upper rev limit.
I still get 40-45mpg out mine on average. It will go higher if i drive at 2000rpm every-where and short shift; but it will do less i i run it around at 4000rpm in every gear.
I would say consider your costs carefully. A diesel commands more money than a breathed upon 180 as standard, if you have had one looked after with the basic mods done then it will get a little more expensive still.
You'd have to do a lot of miles to make the fuel saving in purchase price alone... even if you sell yours for a good price...
I love my diesel (when it runs right) and I have in intention of swapping or selling it, but i dont think that I would go from a 180 to a derv and not feel dissapointed. the noise is something else, and the much higher rev limit is addictive....
I have considered getting a 180 as well to run, as i am curious and they are cheap as chips at the moment - but i dont need 3 cars, and the little fester is used round the city and I am not sure I could be that cruel to a ZS, my derv HATES doing short trips!
With my new turbo in the pipeline I am aiming once more at 200 ponies - would be cruel to have a V6 that was slower than an old tractor