I think the E46 3-series feels more "nimble" than the X5. By no means is the E46 a light car anymore.....My E30 325i weighed about 2800 lbs, our current E46 M3 weighs a whopping 3400 lbs. Granted, a 2001 X5 3.0i weights about 4600 lbs., so you comparing two different weight class vehicle. The problem with Mercedes is that they make their steering on the numb side and their cars not as nimble. I am always amazed how they can make a SLK, C-class and even a CLK feel like your "lumbering" like an S-class. Heck even BMW 7-series are more nimble than your Mercedes S-class.
I have to disagree with Josh re: E36 vs. E46. First of all, I am a big fan of the 3-series and most the BMW line. The E36 had door panels falling off and a 10 year old E36 3-series seemed to fall apart faster than my E30 (Josh never owned a car longer 1.5322467 years
The material they use on the dash is much better than our previous E36. The E36 has problems with the rear subframe literally ripping itself off (even with street driving only). The E46 is an improvement over the E36.
The steering on the 2001 X5 3.0i is very stiff and little assist. The E46 M3 is a little on the light side.
Anyhow, those loaner cars get so abused, the alignment is probably off.
Nevertheless, I do "feel" safer in our X5 especially in SoCal where everyone drives a SUV or Truck in our area and drive them like sports cars on the freeway
I had one of my friends (who is a big time Porsche fan) drive our M3 and he absoluetly loved it....he stated that our M3 felt more stable than his 993 at 110 mph....I told him, wait till he test drives the X5 at those speeds.
Anyhow, you are not flaming anyone, just make a point that the 3-series feels like a lighter car than the X5.
BTW, the new E90 feels more like a 5-series now (more heft). Juan, you should test drive one of those.