Of all the autobots present, SP killed Ironhide first. Why? Because after Prime, IH is the most fearsome opponent in the whole freaking movie! SP feared Ironhide and chose to shoot him in the back rather than face him honorably. Get it? Ironhide is so powerful that even SP had to resort to cowardice to take him out. SP was afraid of him. To me, thats a tribute to Ironhide's badass-ness!