Is it safe?

Looks Ok
PCIE Frequency Setting to 104MHz. (In some cases this can help maximize BClock)
I Heard That It's Not The Best Idea To Do This And Does Not Really Increase Performance (This Was A Part Of Step 2)

I never overclocked those prossesers but it looks ok, are you using proper cooling? It might be a good idea to see what other people did to get to.

Someone else on tomshardware said that their VCore was stable at 1.325V @4.2GHz (intel says the recommended voltage is 1.35), so keep that im mind also im 99.9% the VCore voltage is the main voltage so make sure it's not to high!

 
My cpu is using the stock cooling fan but the motherboard has silentpipe liquid cooling installed as well. should I invest into a better cooling solution? If so, can you recommend where to get started about that?

Thanks.