Originally Posted by Breck
I saw that but, newegg and several other places say GTX 650 has a min requirement of 400 Wattz
You can trust the OCN PSU Calculator over others for a few reasons. First, OCN isn't trying to sell you a higher wattage, and therefore more expensive, power supply. Second, OCN caters to a specific type of customer: One who demands quality and will not skimp on an unproven PSU. Third, other sites have to account for the possibility that you'll be using any combination of other hardware in addition to the GPU. Finally, the person who made this calculator is well respected both inside our community and in the electronics industry, so you can rely on his advice.
Just make sure that the PSU that you do get is on the recommended list. Read reviews on it from multiple sources if possible, and make an informed decision. This way, you won't have to choose a higher wattage PSU for 'overhead' or any margin of safety; you'll have a quality PSU that will easily handle whatever you throw at it.
EDIT: You can even do a bit of math yourself. TDP for the Q8300 is 95W
and the max power for the GTX 650 is 64W
. Other components in the system will use power, but CPU and GPU are the top consumers in any system. The mainboard will consume some, but the rest is negligible. When I ran the calculator with your specs, I estimated 4 RAM sticks, 2 HDD, and 4 case fans.