Update: The H100i actually didn't fit in my case.
So I returned that and got myself that Intel liquid cooler, where radiator and fan basically replace the case fan.
That cooler is solid, super silent, looks nice (lol LED), and is easy to install; yet I didn't get the results from overclocking I was hoping for. I got to 4Ghz, but the Watchdog issues still persist. Meanwhile GTA V got out, and while that ran better, all cores where maxed to 100% almost all the time and for it to run smooth enough, I had to reduce some settings.
I had to reduce some settings!
So I finally got me that i7-4790K!
It was a bit painful to install as it didn't boot at first; turned out the BIOS update wasn't complete (ME update was missing, whatever that is). At the end I got it running, messed up my main drive in the process and had to re-install Windows, which was not a big problem as I have most of my stuff on the other drives.
So I just ran GTAV and it's a bigger difference than I anticipated. I can max everything out, especially visibility range, and it runs waaay smoother. Also all 8 (4 + 4 virtual) cores are used equally at 50-70%, so hyperthreadding is definititely used. Downloading Watchdogs right now (that one was on the main drive), but pretty sure I'm golden there as well.
So that basically concludes this build; that rig should serve me well for the next ~2years. The next stop on my personal technology roadmap: Skylake.