Well, I just wanna tell you guys that finally figured out the problem and managed to make it work.-
To install El Capitan or Sierra you have to use "nv_disable=1". Once you did all the process and finally need the final touch to get full resolution DO NOT INSTALL any driver or anything, you just need original "NVDAStartup.kext" from El Capitan and replace it at /System/Library/Extensions, then set the config.plist at clover EFI with "Inject Nvidia=true" and delete "nv_disable=1" ( but DO NOT add "nvda_drv=1" and DO NOT select "NvidiaWeb"). That's it. Card will be recognized properly and you'll get everything fully working.
If you have previosuly installed WebDriver, uninstall completely first.
This card is working in Yosemite, El Capitan and Sierra. I'm now gonna test it in High Sierra with this same procedure.
GeForce GTX 275 is actually working if you use this method; if you find problems at install or at boot it's most likely to be because of boot flags for your motherboard (like "Still waiting for root device", "Missing Bluetooth Controller", black screens or panics).
Good luck.