I'm sure you made the best choice - based on your personal needs. Edmunds Inside Line recently conducted a comparison between the X3 2.8 and X3 3.5.
2012 650cic Space Gray/Vermillon Red/Blk.Top(retired)
2011 MINI CooperS BRGII/Lounge Green/Sport/Prem/Connect/Black Xenon/Black Conical Spokes/ACS springs/ACS exhaust/Alta Shorty/Continental Extreme DW
2012 M3 AW/FR NDH2/2MK/ZPP/ZCP/ZCW/752/6NR/OEM CF splitters/OEM CF Mirror caps
2012 X3 35i Titanium Silver/Black ZAP/ZPP/TECH/APPS/Breyton GTS/Yokohama Advan Sport A/S