Not sure what the actual extra weight is but I wouldn't be surprised if it was around the ballpark number you quoted...Then again, it is not ideal for the center of gravity but the X5 is such a heavy vehicle in the 1st place, the % of weight added is minimal. It is very different on a purist sports car for sure, hence the uproar for 997 GT3s in the US as they come standard with sunroof, left it off my C4S
Realistically tho, I just don't think it makes a very significant difference on a road car.

C