The tire would be 3 inches taller than what I currently have mounted on my wifes X3 (28).
It looks like there is enough room to fit, but you won't know until it is mounted.
It would look good
and you would gain 1 1/2 of ground clearance. I like that look of oversized AT tires on a euro SUV.
The speedo will be off, and you will notice the x3 will feel sluggish compared to the 'proper' size.
Let us know how it goes. And I would be tempted to try if it wasn't for the fact that the X3 has newer winter tires.