Originally Posted by
kalniel
The K means that the processor has an unlocked multiplier, which greatly assists overclocking should you wish to try running the processor faster than its rated speed.
For gaming there is little difference between the i5 and the i7 processors, but it depends on your budget - if you have a fixed budget then it's usually wiser to save a little on the CPU and spend extra on the graphics card as that's more likely to affect gaming performance. If you can't upgrade the GPU further then improving the CPU is usually the next most important step.