I did some very un-scientific measurements of the X15 5.0 above with an E70 5.0.

Based on the distance of the fuel-filler door to the back edge of each car leads me to think there is about a 4-5" increase in overall length of the X15.

Using the photo of the "build your own X5" and comparing the photo with the actual specs of the car gets me to an approximate 1/20 scale.

Then, zooming on the photo of the X15 above so that it approximates the size of the E70, the distance between the fuel filler door is approximately 1/4" longer in the photo of the X15. Multiplying that 1/4" by 20 gets 5" in additional length, all of which appears to be behind the rear wheel well.

Again, completely unscientific but there does seem to be a little more "car" behind the back wheel well on the X15 than on the E70.

Could be camouflage but my guess is an extra 4-5" of rear space.

LeMans - any thoughts on my guess?