Kanuc, you described my impression of the 50i engine exactly. In everyday drive mode, its setup almost perfectly for a daily driver. The power is there, but you've got to work a bit to find it and wait a beat for it to come on. In sport drive mode, the engine holds higher revs and makes that power more instantly available. There is still a delay at times, but it seems shorter. I like that bipolar nature for those times when someone else is driving my car, but it would be great to get faster response from my lead foot.
The X6 is my first turbo charged engine, and I attribute this delay to the effect of the turbos. If you look at what they did to the X6M turbos,
http://www.xbimmers.com/forums/showthread.php?t=385221, I'd imagine you need some craftwork like that to get that "magic" you are looking for.
495 HP and 573 PF torque is so intoxicating I still may get it one day myself. Maybe after winter.