Both the i7 2700K and i5 2500K are quad core CPUs based on the Sandy Bridge architecture and have unlocked multipliers for easy overclocking.
The main difference between these CPUs are:
- The i7 has Hyperthreading, the i5 doesn't. This technology can yield up to a 25% performance increase in heavily multi-threaded applications. In lightly threaded applications (like games) there is basically no performance increase due to hyperthreading.
- The 2700K runs at a stock clockspeed of 3.5GHz, compared to the stock clockspeed of 3.33GHz of the i5 2500K
- The 2700K has a maximum turbo frequency of 3.9GHz, compared to 3.7GHz with the i5 2500K.
- The price, the i7 2600K retails for ~£285, compared to £174 for the i5 2500K - so a £111 price difference.
Personally, I wouldn't even consider the i7 2700K. The older i7 2600K is still available, costs £40 less and still has the hyperthreading technology that separates it from the i5 and makes it valuable for highly threaded workloads. The only difference between the i7 2600K and 2700K is a slight clockspeed difference (100MHz at stock speeds) and a big price increase. Considering the 2600K has an unlocked multiplier and can easily hit 4GHz across all four cores using the stock cooler and pretty much any P67/Z68 board then the i7 2700K seems like a waste of money.
Also, with this in mind - the i7 2600K would also be a waste of money if you didn't make use of hyperthreading - so if the most demanding task you plan to undertake is gaming then please go for the i5 2500K and use the money you saved towards a better case.
Apart from the CPU issue, its a nice build.