The Pentium Extreme Edition 840 has two physical cores both operating at a frequency of 3200MHz (3.2GHz).
As to overclocking the processor it will require a good amount of cooling as the thermal output is very high, the reason why it is so high is simply because there are litteraly two Prescott cores on one dye, that means lots of heat.
The processor itself is rather unefficient like its Prescott/Prescott 2M counterparts (6 operations per clock cycle vs AMD's 9) so it does not perform extremely well in some things, even AMD's dual cores give it a run for its money and even beat the processor at major multi-tasking which is what Intel usually has the lead on.
If you are not after some extreme multi-tasking then I would recommend going for a single core as they can run cooler and actually work a bit more efficient because they don't have to work with multi-threading as much. The 600 series by Intel is a much better way to go if you are after pure gaming performance
Still its a very fast processor in some applications because as well as having two physical cores it also has two logical cores (so four cores in total). Nice amount of cache and some good features as well