I got one from Big Lots as well. It doesn't seem that out of scale with the rest of my 1:43 but otherwise I couldn't say. I did read where the real thing is so massive and heavy (bullet proof everything) it is actually built on a truck frame and for visibility/security it is slightly taller and more angular than the original Cadillac design. You might find this interesting:
http://www.telegraph.co.uk/motoring/news/4291006/Barack-Obama-new-presidential-limousine.html
http://www.telegraph.co.uk/motoring/news/4291006/Barack-Obama-new-presidential-limousine.html