The wattage of the PSU isn't sufficient information to answer your question. Please provide the manufacturer and if possible the no kidding part number so it can be examined more closely and provide the information you require.
I would go with the 2500k, most games cant use more than 3 cpu cores and only a few use all 4, the extra 4 ht threads will be wasted and unused. Its $80 to get the ht feature over the 2500K, for a gaming computer both cpus are about equal.
I would put the $80 towards a new case, ps, hdd so that you dont have to take the old computer apart, it looks like its still pretty good and would be easy to sell or it would make a decent second computer.
ssd- solid 3/agility 3 60gb
i agree i5 2500k
hyper 212 plus (wont need much more) maybe scythe mugen 2 for 40$ at newegg it is better than that v6 and hyper 212+
what resolution are you playing at because this card beats the 6950 at 1080p and 1920x1200 in both single and sli/cf- http://www.amazon.com/gp/offer-listing/B004XUCCRM/ref=d...
mobo- asrock p67 extreme4 better and cheaper than that msi