i5-2500k is a much better choice, especially if you want your system to last longer. When new processors come out the previous generation will always be slower, however with overclocking you can match the current speed of the new processors.
get the 2500k its better and its unlocked. so you can overclock it and you wont need to upgrade as soon. the 2400 is a waste of money just pay the extra 30 bucks or whatever and get something thats not a teeze