At this very moment considering only the games on the market right now, the 2500k is all anyone really needs to get for gaming purposes.
However, it isn't 100% future proofed. If at some point the game makers create a game that can use more than 4 threads the i7s would surge ahead of the 2500ks in performance.
That time may not happen until such a time as it is time to throw the 2500k in the trash bin anyway, there is no way to know that ahead of time. It is also possible that such a game is going to be released quite soon and then all the 2500k owners are sad about it.
Anyway, I normally suggest to live in the moment and on that basis I wouldn't advise people to avoid the 2500k in favor of the i7s, I just wanted to point that out.
For games that exist right now, a "worse" processor and better video card will likely perform better than a better processor and a worse video card.
That being said, the way games have been going lately it is to increase the demand on the processor more than they increase the demand on the video cards (AA in particular punishes weak processors a lot). Just sayin.