A Haswell, Skylake or Kabylake will give you massively higher minimum FPS than a 2500k at stock.
But oc'ing the 2500k is free, and the difference oc vs oc is much less than stock vs stock. At least from what I've heard/read.
The general consensus here is that it's just not worth upgrading a 2500k/2600k, not yet at least.