If you have your old LGA775 motherboard that can work with 1333/1600 MHz bus speed - buy XEON LGA771 with 12mb cache and higher clock speed and mod it with 2$ adapter available from ebay you will get around 100hs from your old clunker.
https://www.google.com/search?q=lga%20771%20to%20775
https://www.ebay.com/i/282676056978?chn=ps
https://www.ebay.com/itm/Intel-Xeon-X5460-SLANP-Quad-Core-LGA-771-775/162788930733?hash=item25e6f9f4ad:g:ygMAAOSwrFtaIvHT - not the cheapest and not the fastest. If you have c2d extreme 3,6ghz/12/1600 - thats the way to go, but its not cheap at all, xeons are much better choice, there are even lga775 xeons available, you wont even need to mod anything.