Which OS should I go for on Mid 2011 Imac?

[Paramods]

I have a 21" Imac Rocking 20gb Ram and 480Gb SSD.
Im now going to add a Nvidia K1000M GPU

High Sierra is the highest it will go naturally but I would like to go up on the OS as some of the apps I used are no longer supported.

Which unsupported OS will be the best option for me?

Thanks all

 

[mdgm]

I have a 21" Imac Rocking 20gb Ram and 480Gb SSD.

Nice.

Im now going to add a Nvidia K1000M GPU

That's on the list here: https://forums.macrumors.com/threads/2011-imac-graphics-card-upgrade.1596614/

AMD options are better if you can find them as Apple has dropped Nvidia drivers in Monterey making efforts to patch older systems to run Monterey more difficult. Even if Nvidia cards work in Monterey it may be even harder or impossible to get them to work with a subsequent Mac OS release.

High Sierra is the highest it will go naturally but I would like to go up on the OS as some of the apps I used are no longer supported.

Which unsupported OS will be the best option for me?

There is beta support for using the stock Terascale 2 GPU with Big Sur using the latest OCLP. So if your stock GPU is working and you'd like to try a newer OS without a GPU replacement that's the OS I would try. See https://forums.macrumors.com/threads/macos-11-big-sur-on-unsupported-macs-thread.2242172/

A Metal GPU would be expected to give a better experience with Big Sur than the stock GPU.

If you want to put a Metal GPU in then you could try Mojave, Catalina or Big Sur and maybe even Monterey.

Mojave is the last Mac OS to support running 32-bit apps, if legacy 32-bit apps are important to you.