I went a little over 130mph with an 04' 4.4 X5 on my speedometer last night on the 405S. Yeah it was rock solid, and I was pretty confident enough with it. 110 mph cruising limit speed would be great I don't know why you would feel less confident on a 4.8 IS. At 130mph+ the X felt that it had more punch to it, but I never had enough road and the safe opportunity to max out the full potential of the engine.

BTW, maxed out a 2000 4.4 eurospec x5 at 220 Kmh. It should be better for the newer 4.4 engines.