sounds like the bmw sales guy doesn't know what he's talking about. even on your door it says you can run those tyres. even in the manual it says you can.
do as others said and upgrade without a worry... sport package and 335, lol.
'14 Black F11 530xd - NOW
'07 Silver E86 Z4 Coupe 3.0si - SOLD '16
'07 Blue E90 325i - SOLD '12
'06 Silver E90 320d - SOLD '10
'98 Blue E36 320i - SOLD '06