I like the idea of headroom, so I usually aim for 70c max just for that safe buffer.

I used to consider and test "load" temps to be when I was running a synthetic stress test but anymore I don't feel those are a good test.  They are worst case scenarios with an artificial load that many people's machines won't see 99% of the time so I just run a game for 30 minutes and monitor temps to get a "real feel" of temps.  I can easily make my machine hit 90 with a synthetic but during real world use I am in the 45-50 range.  That said it seems with each generation and die shrink the max temps go down.  With Skylake I think throttling starts around 90c so I wouldn't even want to come close.  I'd agree with Scarlet and try to keep it around 70-75 that way if it does overshoot there's a safety margin.

Here are my temps after a 1 hour realbench stress test with my 5960x @ 4.4GHz... 
 

 
66.5c averaged core temps which is just under the max allowed tcase temp for the 5960x. 
 
You should try to do the same with your 6700k. Tcase temp for the 6700k is 64c.

I have my 6700k @ 4600mhz. At 1.30 vcore. When I run intel burn test at maximum setting I get a max temp of 76c under load. I am using a noctua NH D15S cpu heatsink. My temps at idle are 21-26c. When running prime95 I get a max of 72c under load. These temps are all at 1.30 vcore and LLC of level1.
 
Running Intel Burn Test at maximum should weed out any instability. I thought I was golden at 1.28vcore and then realized I needed 1.30 to pass max setting on Intel Burn Test. Thanks HardOCP!

63C on cores at max load for post Sandy architectures IMO.
 
On my 3820 I see roughly 59C load.