Alright ... its time for my favorite game ...
Using the web page at:
http://www.lpl.arizona.edu/impacteffects/
And inputing my favorite data: It impacts sedimentary rock, 50 mi away, it is made of porous rock, wikipedia's dimensions aren't false, etc. and the page's default assumptions, hit calculate and ... Meh, results are not very inspiring.
Now strap some ion rockets to the back and get it going at relativistic speeds, now we're having some fun