I'd go with whatever has nice thick spokes. Xi has jacked up suspension, fat rim spoke will offset that nciely. Dont get deep dish as well. M6 reps sound like nice wheel, but id go for full silver, not black-silver design.
'98 Avus Blue 320i - SOLD '06
'06 TiAg 320d - SOLD '10
'07 Montego Blue 325i - SOLD '12
'07 Z4 Coupe 3.0si - SOLD '16