I test drove one of these (X1 Xdrive23d) yesterday and I gotta say, I'm having serious thoughts about changing out of the 135i.
I don't actually think the X1 is too small. For me, I think the X5 is huge so the X1 seems decent. Means I can throw mate/parents in the back without making them climb in, open the hatch and throw the dog in and dawdle down a (relatively mild) beach track.
I was impressed at how easy it was to drive, visibility a lot better than the 135i due to the height, hung onto corners pretty decently for what it is and the engine definitely has the same 400Nm of torque my 135i has, although it comes on a little later and doesn't last as long. It still shifts along nicely and despite being the demo car, which has been flogged since day dot, it was only averaging 8.5l/100.
I spec'd up one to about $83K on road but that had a lot of options ticked for that money. Tempted, sorely, sorely tempted.
Proud new owner of a X1 23d in Jet Black