Take a look at this thread:
I recommend 275/30/19 in the front - but you will need to remove the camber pins and add negative camber for them to look right.
Who sold you et8 rear wheels? That offset seriously limits your tire options. I don't know what tire size will work without rubbing... I guess you could try 275/30 or 275/35. No matter what you do that wheel width / offset will look ridiculous.
'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?