 First let me say, that if you own a 2005 to 2009 Mustang GT you own something truly unique.  I had a 2006 GT and a 2008 GT and in a way I wish I still had my 2006.  Here is why: the look, feel, sound, gauges, dash, air conditioning registers on these years were retro and perfect and will never be duplicated again.  Now about the 2010 GT, why would I buy a 2010 GT instead of a 2011?  Proven and Perfect Motor, Proven and Perfect 5 speed, Proven and perfect steering, you can use 87 octane, the car is too fast and too quick for 95% of urban driving.  What you have here is the perfected article.  The safest, most reliable, most proven design to date.  If you want the quickest get the 2011 5.0