I did the same thing...traded my X5 after less than a year for an M3. I also really liked the X5 but just didn't love it (nor did I enjoy washing it), yet I still worried that I'd regret selling it. That turned out not to be an issue at all. I LOVE my M3!!

To the OP, good luck with the M5.

__________________
2009 E90 M3 M-DCT | Alpine White/Black/Carbon

SOLD: 2008 X5 3.0si | Black Sapphire/Black Perforated/Burl Walnut | Premium | Sport | Cold Weather | Premium Sound | Active Ventilated Seats | Auto Tailgate | Comfort Access | Running Boards | Heated Rear Seats | PDC | OEM 20" Style 214s | Titanium Kidney Grilles | Tint 20% Rear/35% Front | GP Thunder 7500K Halos | Xenesis Fogs