Hello. New user there.

Since you mentioned X3 stiffness...

Just turned in my lease '08 E92 with Sport Package and got '08 M-Sport X3si yesterday.

Coming from one sport package straight to the other one, I can tell you that they are of identical stiffness and both are pretty stiff.
Perhaps an X3 without sport package and 19" wheels may be much softer.

What did make my E92 softer, was aftermarket wheels with non-RFT tires. It was a night and day difference.

Unfortunately it is at 3,800 pounds unloaded, so it is well over 4K with gear. Has around 450 pounds of tongue weight. I actually think that with proper weight distribution, the X3 would tow it safely (I have a prodigy brake controller on the X3), but would I'd have more trouble keeping with the flow of traffic on mountain passes for sure.

Our X3 has towed a 3,000 pound camper in the past and it was well balanced and still returned decent mileage. Manual gearbox meant I could always keep it in the right rev range. Notably, even with a fair amount of tongue weight, the X3 barely sagged at all! In fact, ride comfort on my somewhat firm riding '04 is close to perfect when you load up the suspension with a substantial trailer! Remarkable vehicle.:thumbup:

We have an '06 X3 with 42k miles on the ODO. It's been a great ride and we've reached up to 28mpg on nice flat NM roads. It's nimble, sounds great, accelerates well, is smaller but good interior space, seats are firm but comfy - love those seat warmers. Could not get the wife to sell the car for all the tea in China! Firm ride? - yep. Too firm? Ever driven a true sports car? Would not think of towing with it - that's what the big dog Ford is for. We've had zero issues so far. Overall, we'd tell you it's been one of our favorite automobiles to date. Good luck.