Well I can put some useful info into this but it has to do with the 2005 with xdrive and the e70 with xdrive.
When we had our last real snow (the one where the tree was so snowed over I couldn't tell it was blown over and pointed straight at my front windshield and busted the windshield if anyone remembers those posts) the xdrive with all season tires never had any issues with the ice or the snow. I actually used it to pull a Toyota 4wd truck out of a section of a parking lot and he had very aggressive tires but was just sitting there and spinning. The xdrive had no issues at all pulling into where he was stuck and pulling him out. If fact I parked where he was stuck to go into the store to get my carton of cigs
I have owned around 12 or so 4wd trucks and the xdrive has impressed the CRAP out of me. I have had the right front tire off the ground and the left rear tire off the ground at the same time and it just paused a second and went on.
That said my 2001 x5 is pathetic in comparison at the moment. I wouldn't trust that thing to handle pine straw on the ground if it was built up any under trees.
But in its defense the abs isn't working on it. The way it is right now the drivers side front tire and one of the rear tires (cant tell which one) loves to spin and when they do it just sits there.
But again the abs isn't working. Once that's fixed I will have a better idea of what it can do.
But as for snow/ice at least with the xdrive it was amazing. I never had any issues with it going where others were getting stuck right and left. Would snow tires of done better? Maybe but I never had a situation where I thought to myself "damn I wish I had snow tires for this". I did hear the abs a few times while coming to a stop at stop signs and red lights. Never felt the car getting out of control just the noise of the abs doing its thing so something slid somewhere.
To me the real test of awd and 4wd is mud. Ice is bad but snow isn't as bad a problem moving wise as clay mud. Nothing is slicker than that stuff. THATS what really makes the xdrive shine around here the most.
I run cooper ultra cs5 tires on the 2005 x5 and pirelli verde scorpion all season run flats on the e70.
Both had done great for me in the mud/snow/ice.