The 9450 will overclock farther because it has a higher multiplier and wont force you to run into the high 450+ FSB area like the 9300 will. If i recall correctly the 9300 is a 7.5x, the 9450 is 8x and the 9550 is 9x. Personally if i decide to upgrade from my q6600 to a 45nm i'm going to pay the extra for the 9550 just so i dont have to run a huge FSB to hit 4ghz.