Personally I feel the X5 3.0 is underpowered, or rather, overweight. However, I'm a bit skeptical with regards to 'doctoring' the engine due to reliability issues. Further, the wifey drives the car most of the time, so I think the extra shove is waaay down her priority list.
If only the Malaysian roadtax structure does not punish high cc engines... The X5 4.4i would've been closer to perfection..