just saying for the build, you will not have any benefit of z68 whe you are not overclocking. get either a h67 board or a h61 board. also, if you want 4 gb of ram get a 2x2gb kit since the system doesnt run very well single channel. you must get dual channel.
as for the power supply, does it have enough amps for the graphics card? if it doesnt, get a higher wattage or a different unit
should just be enough be careful with the cm storm scout i have one they are an awesome little case but it didnt fit my gigabyte 6950oc with the windforcex3 cooler i had to move the drive bays over a half inch and chop about a quarter inch of the bottom of the 5 1/4 bay. it was very upsetting to do a hack job on a new case i didnt find out till the very end the last thing i do in a build is add in cards after a 2hr install (i go crazy with cable management)
For this specific build? Yes, it would be enough.
"The "recommended" watts Sapphire recommends is 500W, because they do not take it account of 80+ certificate, and the one you chose, is certified as 80+ Bronze."
However, I think most people would not recommend it. The ultimate purpose of having an after market cooler is to OC, even just a little bit...
Would definitely suggest not to go for i3 + Z68 combo... Because... Well, you can think of the rest.
That version of the XFX Pro 450W Core Edition only has one PCIe connector. A 6950 needs two PCIe connectors.
Jasont78 makes a good point about the length of the graphics card. The Cooler Master Storm Scout has a below average GPU clearance of 28cm.
The two Sapphire 6950s that I can think of atm are only 26 and 27cm, but you should definitely double check that the version you are buying is less than 28cm long.
You also have to bear in mind the location of the power connectors, as if they are on the end of the card then they increase the effective length of the card.