I am buying this used 540i for a very good price and even with all mods (stage 3), much cheaper than a used M550 with same condition, options...
Also, I attend to use the 540i as a daily and it is a lot cheaper to drive in term of insurance, fuel consumption...(at least here, in Switzerland) than a 550i knowing that I have around 80 miles per day just to go and come back from work.
I honestly also like the fact that I will put my hand on it to improve it and have already the M4 ZCP and M5 ZCP ready made for fun
.