well you stock heat sink will work...but you must remember that the q9400 is a 95W processor as opposed to the 65W e7300.....so there will always be a high possibility that the processor will heat up quickly
you don't need to...you will be fine with the existing one.
although....having the latest bios does you no harm
& will my current stock hsf of my c2d e7300 work the q9400 ? or will I need to buy a separate heat sink fan for it? & No I don't plan to oc the cpu , I plan to use it for casual gaming paried up with a gt 440
well you stock heat sink will work...but you must remember that the q9400 is a 95W processor as opposed to the 65W e7300.....so there will always be a high possibility that the processor will heat up quickly