Not sure about the LED's I'll let someone else answer that but in regards to fuel anything north of 91 Octane or 98 in Europe is OK. You can get a propane conversion kit for the X5 which you can run it on propane or regular gas but you lose the spare tire space for the propane storage.

__________________
Currently 2010 X6 35i, Premium, Technology, Sport.
2004 Lotus Esprit - Final Edition
Former '04 X5 4.4i, Highland Green, Nav, DSP, PDC, Heated FR & R Seats, Comfort Seats, Rear Load Floor, Premium & Sport Package, IceLink Plus, Bel RX65, Tow Hitch, Sirius Satellite Radio.
Former '03 X5 3.0, Nav, Premium, Rear climate. (Stolen)
Former '01 X5 3.0, Nav, Premium, Rear Climate (Lemoned)