You are correct, depending on the drop you could align within specs. I don't know how far you went. If you have the capability to crop your pictures or reduce the resolution you should be able to post pictures.
Not saying coilovers won't improve handling if for no other reason than you can lower the center of gravity. I am saying that coilovers are only one of many components needed to "significantly" improve the handling of an X5.
My limits on the street are just inside of being dangerous to myself or others. That is well within the capabilities of my suspension mods. The 4.6 handles quite well as delivered though has very little similarity to a BMW car. My goal was to move as close to that 'feel' while still having a Dollar spent per handling improvement equation that was logical to me. I felt that the money spent on the coilovers I would consider would result in a far better value equation if spent on more HP/TQ. For clarification only, the comparison of H&R lowering kit is not $950 to $1,000. It is $375 to $950. Rebuilding the suspension is mostly separate expense.
If I were to start over, the first thing I would do is find Eibach front and rear sway bars. That single change was a big one. The result was a much improved turn in and less body roll. I would purchase spacers to widen the stance and get an alignment that was at the spec limit of negative camber. Tires will wear faster but--. I think these things are universal rather than specific to a 4.6. Benefits from strut tower brace, camber plates, HD struts and shocks were noticeable but not as much as the first changes I mention. I upgrade some of the suspension but I think it made feel good more than anything else. I really like the looks of a lowered X5. I have two wheel air suspension and it works fine so I had no interest in removing it. That was a significant factor in the choice of H&R lowering kit. If I were to go to coilovers now I don't think I would consider those that don't have adjustable rebound rate and damping as coilovers that would more out of other things I have done.
I have attached a link to a youtube video that may worthwhile watching if someone is considering a lowering kit or coilovers.
https://www.youtube.com/watch?v=biOLaKSC0sM