I had a client this weekend who wanted to upgrade a couple of the family PCs without "breaking" the bank. The were running an aging 775 socket and checking around I found this.
http://www.delidded.com/lga-771-to-775-adapter/Long story short I managed to pop a couple of Xeon 5450 into their 775 boards, pop in a couple of cheap SSDs and their systems were 'flying' again.
A great option for those that don't want to buy a new pc but want something fast with quad-core.
