Referring especially to the E8400-E8600 dual core 2 cpu's.
While they are several years old now they can be overclocked to run over 4 GHz giving them performance well beyond the stock specifications.
Obviously the cpu architecture is superseded and they run on the old DDR2 RAM but with a bit of extra voltage they can closely trail in performance to the newer i5s in most games (with the obvious exception of the most resource intensive - like Crysis 3)
This article here is a couple years old now but it's still fascinating to read
http://www.tomshardware.com/reviews/ivy-bridge-wolfdale-yorkfield-comparison,3487-21.html
Quoting from the article
In the end, we're impressed by the staying power of Intel's Core 2 architecture, especially the 45 nm CPUs tested today. But we’re also saddened that Intel no longer sells budget-friendly processors to enthusiasts, like so many Celerons and Pentiums from the past. While the company clearly made big improvements to threaded performance, memory bandwidth, efficiency, and value-added features, it's a little disappointing that an overclocked Core 2 Duo from four or five years ago can match or beat today's best dual-core offerings. Of course, we're keeping in mind that the E8400 original sold for almost three times as much. But still, it would be fun to disable two of Core i5-3570K's cores and see how a K-series Pentium might have performed.
While they are several years old now they can be overclocked to run over 4 GHz giving them performance well beyond the stock specifications.
Obviously the cpu architecture is superseded and they run on the old DDR2 RAM but with a bit of extra voltage they can closely trail in performance to the newer i5s in most games (with the obvious exception of the most resource intensive - like Crysis 3)
This article here is a couple years old now but it's still fascinating to read
http://www.tomshardware.com/reviews/ivy-bridge-wolfdale-yorkfield-comparison,3487-21.html
Quoting from the article
In the end, we're impressed by the staying power of Intel's Core 2 architecture, especially the 45 nm CPUs tested today. But we’re also saddened that Intel no longer sells budget-friendly processors to enthusiasts, like so many Celerons and Pentiums from the past. While the company clearly made big improvements to threaded performance, memory bandwidth, efficiency, and value-added features, it's a little disappointing that an overclocked Core 2 Duo from four or five years ago can match or beat today's best dual-core offerings. Of course, we're keeping in mind that the E8400 original sold for almost three times as much. But still, it would be fun to disable two of Core i5-3570K's cores and see how a K-series Pentium might have performed.