I use the "M" factory oil during the summer months here in Texas. With the 100 F degree days and boat towing, the added viscosity is comforting. Additionally, oil consumption is about 2500 miles/quart. With 5W-30, consumption is more like 1500 miles/quart.

2002 X5 3.0 258,366 miles
2004 325i 114,000 miles