Is there any difference with the I5 4670K and the I5 4670 when not overclocking?
Yes slight differences http://cpuboss.com/cpus/Intel-Core-i5-4670K-vs-Intel-Core-i5-4670
But if you are not OCing, the 4670k is definitely not worth the extra money
No. The k version has an unlocked multiplier. That's it
No. Only difference is that the non K has all the cores locked. And the non K is a little bit cheaper.