I would not put anything wider than 275mm on a 9.5" wheel. A wider tire will not have good support. I would also not even consider the et35 wheel as it's too far off the correct offset for an M3. Especially considering that Volk makes their wheels with some of the best M3 offsets (no spacers required). There are plenty of used Volk wheels available on this forum. Keep your eyes on the wheel/tire for-sale section.
'08 E90 M3 - Alpine White - Sold
'13 E92 M3 - Silverstone II - Sold
'04 E46 M3 - Jet Black - BBS E88, KW Clubsports, Brembo BBK, SuperSprint Exhaust, Recaro
'15 i3 - Laurel Gray - Why would I mod this thing?