The only difference is clock speed yes. A slight difference in clock speed out of the box and the k version having a factory unlocked multiplier. It doesn't come with a stock cooler, the plain 6700 does come with one. Intel likely assumes enthusiasts will go for the 6700k and tend to use their own aftermarket cooler anyway. Especially if planning to overclock it.
Out of the box, the 6700 turbo boosts up to 4ghz. The 6700k turbo boosts to 4.2ghz. Overclocking isn't guaranteed, most chips overclock decently. Some better than others, it comes down to the actual cpu however there's a good chance with a z series motherboard and decent cooling it should be able to reach 4.6-4.7ghz or perhaps higher. In that case the 6700k means 600-700mhz better clockspeed.
Everything else about them is the same, same igpu, same amount of cache, hyper threading etc.