I diagree. I did the exact same thing myself after reading up on it intensively. I read in a lot of places including http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=3730 that there is a pretty decent chance the cores will unlock. The consensus seems to be that around 70% (give or take) will unlock all 4 cores.
I say go for it if you can accept there is a chance it wont work and you will only have a pretty decent dual core. Just make sure your motherboard has the bios settings to unlock. I have a Gigabyte GA-MA790XT-UD4P which worked like a charm.
I looked at your selected psu and maybe you should consider changing it to a decent 80+ certified one. I dont have the expertise myself to recommend one, but look around the forums, there are plenty posts discussing good psu's.
I have a Phenom II 720 and it couldn't unlock the fourth core(gigabyte Ga-ma_790fxt), Roverjoost said that there's a 70% chance that you can unlock the 2 other cores I would say its less then 25% chance.
At that point the Phenom II 955BE really doesn't cost that much I'd just buy it an get a good quadcore without any risk and without voiding your warranty