If you don't want to Overclock then why get "K" Processor ?
ocing with caution and right cooling can really effective and increase performance significantly.
Regarding gen4 it has new socket so you might need to change motherboard/upgrade to lg1150 support one.
One major difference is that at normal Idle State the 4th uses less power.
For More Benchmark Test see (http://cpuboss.com/cpus/Intel-Core-i5-4670K-vs-Intel-Core-i5-3570K)