They are two very different processors. In fact the 6700k is faster on a single core basis. The 6950 gains its advantage in the number of cores (10) vs 4. Better investment?
The better investment is the one you actually need. Gaming wise the 6700k is faster. There are 0 games that will use all 10 cores and while we have been promised for years that will happen, it isn't looking like that will change.
As for rendering, if you are a hobbyist the 6700k is fine. If you are doing some serious work like its your job, then you may want to consider a $1600 processor. But thats the only reason to consider it. Both of them will obsolete for their respective tasks in due time, with no advantage for either.