Switching to the 4790K is also going to require you to buy a new motherboard -- FX-8120 is AMD's Socket AM3+ (pins on the chip), i7-4790K is Intel's Socket LGA 1150 (pins in the socket), so they're 100% incompatible. So, if you were worried about spending 100 EUR on RAM, just realize you'll probably be spending twice on the new motherboard...& then you'll have to make sure before you install the new motherboard & CPU that you've taken the time to back up your essential files, since you'll need to reinstall Windows on your hard drive -- assuming, of course, that you're not using an OEM machine (Dell, Gateway, HP, etc.), where the Windows key was tied to the original motherboard. If so, that's another 100-150 EUR for a new copy of Windows.
Out of curiosity, is there a particular reason you're wanting to upgrade (i.e. poor performance), or just because it's an "older" system & you wanted to start fresh? Depending on your current motherboard, it's possible that you might be able to replace the CPU. Your current FX-8120 has a 125W TDP, which is the same as the later FX-8300 series of chips, so your motherboard could potentially handle anything from the FX-8300 (currently running about 116 EUR, & still one of Tom's Hardware's mid-range CPU picks, http://www.tomshardware.com/reviews/best-cpus,3986.html) to the FX-8370 (currently running about 175 EUR). Tom's Hardware ranks those chips at the same level as Intel's Ivy Bridge Core i5 chips, or their Sandy Bridge i5 & i7 chips, which puts them 2 steps up from your current chip & right behind the i7-4790K in their rankings (http://www.tomshardware.com/reviews/cpu-hierarchy,4312.html)...&, based on a lot of the games released over the past year, the FX's performance not matches up quite nicely with those same Sandy Bridge/Ivy Bridge chips, but isn't too far behind the Haswell & Skylake chips (or at least only far enough behind that you'll only notice the difference if your monitor refresh rate is well over 60Hz).
Also, depending on your motherboard, you have the potential to even OC your current chip & get some increased performance from it. Aftermarket coolers are fairly cheap -- should run you about 40-50 EUR for a mid-range air cooler -- which should allow you to pump that FX-8120 up quite a bit (maybe even up to 4GHz). That's also an option if you just decide to get one of the newer FX chips.
Of course, the other issue is that I see no mention of your GPU. To be honest, even a Skylake i7 is going to give you fits if you pair it with a weak GPU -- for example, slapping in a GT 730 (or even a 1GB GTX 750Ti) means you're not going to get a lot of boost, even with an i7-6700K. If you're having performance issues, it's possible that your GPU could be holding you back, or even something else entirely: thermal throttling on your CPU and/or GPU, Internet connection problems, etc. And again, simply swapping out for a new motherboard & CPU won't fix those kinds of problems.
Facebook
Twitter
Instagram