X5 is great - if I had to give up one, I would give up the Rover since my wife would drive it mostly. Drove both versions of the 12 RRS - I did back to back and the HSE is pretty impressive now - almost the same HP as my 08 Supercharged. The new supercharged is a beast though.
I am getting the 35 with the Msport for my wife. She didnt want the X5M so I told her she couldnt have the 50i since they are so close in price....lol Flash of the ecu and she will be back to the same power as the 4.8
Good luck with the purchase!