I would say that your budget will be your guide. As far as I am aware, all 550s are basically the same. '07 and '08 really are the same, I think. Different wheels may have been offered for '08. '09 brought a slight facelift, with a different grille, new steering wheel (the biggest improvement, IMO), updated COMMAND system, new rearview mirrors (the old ones were prettier, IMO), new full LED tail lights, and restyled tailpipes and rear bumper (I like the earlier oval tailpipes more than the newer rectangular or trapezoidal tailpipes). I am not sure what was done for the '10 and '11 model-years. If the price is your primary concern, I would look for the best combination of price, mileage, and condition in an '07 or '08 (I just paid a month ago $36,800 for an '07 with the P2 package and electronic trunk closer with 23,000 miles in perfect condition from a BMW dealer). I don't think I would bother with a '10 or '11. If you really want the facelifted version, I would stick with an '09, and I would look to spend somewhere between $45,000 and $48,000. The '10 and '11 are still probably too much to be worthwhile. They will likely take a bit hit when the new one comes out this summer. Hope this was at least somewhat helpful. Good luck with your search and let us know what you end up with.