iMac with NVIDIA GeoForce GTX 675MX question

[Racineur]

Hello, I have an i5 late 2013 iMac with NVIDIA GeoForce GTX 675MX and 1024 MO. My set-up: internal 1 TO FusionDrive with OS X Mountain Lion (original). External partitioned external SSD with El Capitan 11.11.6 and High Sierra 10.3.5. External HD with Sierra 10.12.6. iStats shows that the load on the GeoForce increases with each OS. Capitan being the least demanding, High Sierra being the most of course. Since the iMac is slowly becoming a dinosaur, do you think it would better to settle for El Capitan because of the lighter load on the GeoForce? Note that I don't see and feel diminished video performances with either OS. I'm just trying not to be too demanding on my old iMac which has worked flawlessly since day One. Pictures attached.
Thanks a lot for your cues and help.

 

[gitresethard]

Hi, I personally owned that same iMac model with a GTX 675mx. I even remember playing Arma 3 and Skyrim on that machine. I think the GTX 675mx is better than the GT 750m I had on a late 2013 mbpro 15", and I was running High Sierra at 2880x1800 (using quickres) and it runs very smoothly, even with an external 4k monitor.

I think your machine is more than capable of running High Sierra, and I think those iMacs have a max res of 2560x1440 if I'm not mistaken, so I wouldn't worry about it.