Mr.Mago

So, it’s been a while but I have some results!
 
So I overclocked the RAM from 2133mhz to 3000mhz, installed a second SSD (512GB EVO), got rid of NVIDIA GeForce Experience, tweaked some settings in NVIDIA Control Panel, disabled some Windows Services and started using Intelligent Standby List Cleaner.
 
WELL SWEET LORDY BABY JESUS, MARY AND JOSEPH!
 
The amount of games that I can run on either a solid 30 or 60fps has tripled in an instant! Guess it was me been stupid with how I was changing settings!
 
I have ordered in 32GB 3200mhz memory to accommodate for Final Fantasy XV been a memory hog at 12GB (without the 4K Texture Pack) and plan to overclock it to 3466mhz (which is the max the mobo supports)
 
Thanks again for all your help! It was highly appreciated!

Thanks a ton Mr.Mago for your help!

If you plan to keep the motherboard you should: upgrade to 16GB and buy a 4th gen I7. Like a 4770 or a 4770k, if you plan to go for the overclockable version check if your mobo has a good vrm and you have a CPU cooler so you can put the 4770k to 4.5 or so

There are no physical drive bays in this case. The mounts are "tooless" and have nothing surrounding them when not in use

https://www.youtube.com/watch?v=myS3bC6BvdM
 
So the GPU will fit, it will just have to be maneuvered into around the front HDD plate

E5520 is rock bottom.
If you are willing to update the EFI on the mac pro, it is possible to upgrade it all the way to either the X5690s (6x3.46 GHz x2), a pair of x5687s (4x3.6 GHz x2, cheaper) or x5675s (6x3.06 GHz x2, about the same as the x5687 but slower single core)
 
However, there are some problems with these mac pros. They were running their CPUs without lids for some odd reason; so you would either have to delid the soldered xeons (you can find a couple guides on youtube on doing it, if you go this route try some cheaper xeons first) or use washers (https://forums.macrumors.com/threads/4-1-processor-upgrade-install-help.1701420/#post-18710268). You can also find some overpriced already delidded xeons on ebay if you want.
 
Those xeons I listed should be able to keep up with a HD 7970/ r9 280X easily, above that its gonna be close at stock clocks. The PSU is a 980W unit and should be capable.
 
RAM upgrade is a no brainer, 16 GB in 2 GB DIMMs are really cheap on ebay. Alternatively, 8x4GB kits of ECC specified to work in the Mac Pro can be found for about 100$ on ebay, with 8x8 GB kits costing about twice that much. 
 
Oh, and if you don't have an SSD yet get one.

Alright, thanks for the answer, but I still dont know how can someone get 2500 score with an i7-4770k xDDD

I get around 5k in Physics at 4,6GHz-4,5GHz. But I also run RAM at 2200MHz CL9 and Firestrike is RAM sensitive. So your score prety mutch matches mine if I run 1600MHz RAM.

I was using 1.3V and 93°C max in OCCT, 70°C-80°C in games for a year, then I delided and upped the clocks and voltage, now I am at 85°C max in OCCT, 55°C-70°C max in games but 1.38V for over a year.
 
You're way below that so you're fine.