From BMW docs:

Performance & efficiency
• New engines in both models:
---3.0si – N52 6-cylinder engine with Valvetronic, magnesium/aluminum composite construction and other new features; 260 hp/225 lb-ft. torque
---4.8i – N62 V-8 engine, displacement increased from 4.4 to 4.8 liters; retains Valvetronic and aluminum construction; 350 hp/350 lb-ft. torque
---6-speed automatic transmission now standard in both models (previous 3.0i: 5-speed automatic optional, 6-speed manual standard)
---Automatic transmission includes extensive improvements for higher efficiency, quicker response and shifting, and finer adaptation to driving style and conditions
---New-type electronic transmission selector, similar in concept to that of 7 Series but on console instead of steering column
---xDrive fulltime all-wheel drive system, electronically controlled with variable front/rear torque split & traction control

-New technologies enhance fuel efficiency:
• Valvetronic variable valve lift (new to 6-cylinder X5 model)
• Rolling-resistance-optimized tires
• Delivery-regulated fuel pump
• On-demand power steering via electrically controlled bypass valve
• Pentosin power-steering fluid; revised viscosity index reduces power requirement at low fluid temperature
• Improved control of climate-control compressor’s clutch
• New-type rear differential