The N62 has only one weakness, the valve stem seals tend to wear out causing high oil consumption and smoking at idle. Typical cost of replacing the valve stem seals is around R25k. Maybe the later LCI models had the improved valve stem seals, but its best to expect the worst and plan/budget for the cost when buying.
Other than that, they are bulletproof as long as the gearbox oil is changed every 80k km or so.
I drove an E70 4.8i for 10 years and 250k km. It really was an awesome, capable and reliable car in all respects.