as for price milage is the biggest factor in car purchase-but for actual use...
the bmws you mention do miles well-but at 150k ish it may well suffer from the gearbox valve block wear[makes it hunt up and down at steady throttle-and resetting the gearbox softwear wont cure it] that said it doesnt stop the car going a to b-just irritating once you notice it
other than that milage doesnt seem a factor as the common fails happen any age after a few years old-glow plugs,glow plug control units,thermostats etc
the 335/535 d seem a very good buy -easy to get 45mpg out of my 335d

if you go audi-clutches,fywheels,boxes,oil pumps etc after 100k