I would say this for those choosing between the two.
Average together the advantage percents, then find the price difference in percent to see which one is the better buy for the money.
If the percent price of the Q9300 is greater than the average percent advantage, then buy the Q6600. If the percent price is less than the average percent advantage, then buy the Q9300.
Example.
Comparing the prices will depend on where your going to buy either processor from and whether OEM or retail So lets say Ill buy it at clubit, this does not include shipping. Now unfortunately clubit does not have the Q9300 yet, so I will use the price from costcentral on google.
Q6600 OEM: $239.99 (Clubit)
Q9300 OEM: $289.99 (CostCentral on google)
Ok so the average percent advantage the Q9300 has over the Q6600, from the chart posted above is about 6.66% .. So now the Q9300, using the above prices, costs about 20.8% more than the Q6600, So the cost percent is more than the percent advantage, so at least using these prices and the chart above the Q6600 is the better buy..
You could use this math to figure out a purchase for any product.
Of course there are still many factors we have not considered, including but not limited to power consumption, oveclocking ability and motherboard/software support.