It sounds stupid to me that you come to a M3 forum to ask opionion about deciding a M3 and a XK. However, I am happy to be the one to vote for the XK.
BMW 2006 330i E90 Jet Black/Black Leathers/Aluminium, Steptronic Active Steering; MTech Aero Kit Carbon Fibre Splitters/Diffuser. Bilstein PSS9 Coilover, Rays VOLK Racing RE30 Formula Limited Edition 18" Pirelli Rosso; Project Mu 355mm Forged 4pot Caliper. HID:Osram D1S 6000K, PIAA 6500K White Ring, Philips Diamond Vision HB4 5000K, PIAA H490/H491 Super Bright 6500K LED Interior Lights. Chrome S.Wheel Cover, Rear Windows Sunshades.