which motor in the x35 are you referring to? N54 or N55?
for the n54 the only manufacturer plug available is the Bosch ZGR6STE2
the aftermarket solution is the ngk 5992 which is a one step colder heat range plug, these plugs need to be regapped to 0.022 inches to work satisfactorily on the n54, these plugs do not give you any performance bonus but when heavily tuned and running high levells of boost the spark will not break up and splutter...
i hope this answers your question...