W221 s320 cdi or s350 bluefficiency

[satbasi]

Hi, sorry if this is posted under the wrong title but im looking for a w221 diesel. Question is i can comfortably buy a prefaclift but for a facelift will have to stretch

Is it worth spending the extra 4-5k on a car which i will probably sell in a few years?

Also technically are they about the same?