Size wise, even original X3 was bigger than original X5 (INSIDE). The new X5 is huge - in fact, parked next to Q7 audi (which looks like a bus) it doesn't look smaller, it looks same or even wider. Do yeah, X5 is a massive car and not for me, but I know people love how comfy and isolating from world it is.
X1 is quite cheap and cheerful looking car - except it's not that cheap, it's actually very expensive for what you get. X3 or 3 series touring with xdrive seem like better cars. You just overpay for X1 too much given how little car you get (and it's ugly-ish).
Also I believe the current X3 is almost identical in size to old X5!
'07 TiAg E86 Z4 Coupe 3.0si