When ordering my car, I originally researched DHP quite a bit. Originally didn't include it, but after all the interneting and reading specs I ended up adding it in. I can't remember exactly where I read it but I remember seeing that adding DHP lowers the car by 10mm... sorta remember it was about 1cm.
For me coming from an Audi A6 which felt very similar to the 540i I test drove, it was the logic of DHP being necessary to offset the added weight of the V8. I unfortunately was only able to test drive cars without DHP, so I went with it based on internet research and how it made sense to me.
Now that I've had the car for a couple of months and over 2k miles, I'm 100% glad I added it in. The 4-w steering really helps with turning radius in the city and in parking lots... I'm still pretty paranoid about hitting stuff in tight spaces, haven't really got used to the dimensions of the car yet. While the behavior of the car at highway speeds is something to get used to, it feels a lot smoother and well planted than my A6. I usually use the driving assist features in the highway anyway.
Another thing DHP brings to the table is what they call active roll stabilization. Which is basically dynamically adjusted sway bars. For its size and weight, it's surprisingly planted when cornering... eats up exit loops for breakfast.
