If you can spend the extra money go with the 4.8. Its got the new frontend and lights, Although it only has an extra 15 hp. It feels like alot more than that becuase its got the new 6 speed auto tranny which makes a big difference and also air suspension which the 4.6 did not have. And also it gets much better gas mileage than the 4.6 because of valvetonic. But if you are looking to save some mony go with the 4.6is. Almost forgot about the Xdrive which is alot better than the original fwd the 4.6 has

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Dinan M3

2006 X5 4.4i Sport Current Vehicle
2006 CLS 55 AMG Current Vehicle
2010 FORD F-450 King Ranch Current Vehicle
2012 GL 550 Current Vehicle

1999 M3 Dinan S3 SOLD
2001 M3 Dinan S2 SOLD
2002 M5 SOLD
2004 X5 4.4i sport SOLD
2007 335 XI Lease ended
2009 E92 M3 SOLD