There does not seem to be a thread specifically about this subject. I searched and found these X dimensions posted by NigelM in the "configuration has begun" thread (X dimensions are not yet shown on the publicly accessible X web page):
Model X
Length 198"
Height 66.3" (doors closed)
Width 89.4" (mirrors extended)
Ground clearance 7.2" (is that with air suspension on a specific setting?)
Model S
Length 196"
Height 56.5
Width 77.3" (mirrors folded) 86.2" (mirrors extended)
Ground clearance 4.7" to 6.4" (air suspension range)
So the X is 2" longer, almost 10" taller, about 3" wider. Seems to have slightly more ground clearance.
Model X
Length 198"
Height 66.3" (doors closed)
Width 89.4" (mirrors extended)
Ground clearance 7.2" (is that with air suspension on a specific setting?)
Model S
Length 196"
Height 56.5
Width 77.3" (mirrors folded) 86.2" (mirrors extended)
Ground clearance 4.7" to 6.4" (air suspension range)
So the X is 2" longer, almost 10" taller, about 3" wider. Seems to have slightly more ground clearance.