4Ghz is nothing for an i5-2500k. I still wouldn't do it on stock cooling, because the heatsinks are small and the fans are loud, but any decent $30 cooler is plenty.
As far as the GPUs, you need good airflow to keep them cool, and hopefully you have a spot separating them on your motherboard. My top card idles ~30 degrees warmer than my bottom one (mostly because I have 2 monitors connected and it doesn't go into a low-power state), but full usage they're ~10 degrees different, and that may be because my bottom card has a nicer cooler (it won't fit in the top slot).
As long as you're not letting the hot air accumulate in your case, you should be fine.
Superior in its performance, this cooler possesses a copper base, aluminum fins, and three heatpipes which accelerate heat conductivity and effectively transmit heat to the fins. A 9 cm super quiet fan will halp draw heat away from your PC. Besides, tool-free clip design enables an easy installation. Best of all, It provides a comprehensive thermal solution for Intel and AMD systems.