Installed the latest version of Ubuntu MATE on a brand new SSD and slotted it in to my old MacBook Pro recently.
It certainly runs better than OSX did, lately OSX would spike CPU usage and spin up the fans for even basic web browsing. It's an old Core 2 Duo T9400.
There's still some quirks I need to sort out (such as having a standardised copy-paste keyboard shortcut and improving the trackpad), but overall it's working well and I'm happy.
As someone who misses the old iPhoto (why oh why did you replace it Apple? Photos is inferior), Shotwell is awesome. Not having two libraries on my system probably saves a tonne of space too.
Many things that used to require futzing around in the CLI in the early Ubuntu versions I was using back in the day seem to be automatic now.
I'm only using a fraction of the 8GB of RAM in this machine. Weirdly it shows up as 7.5GB of RAM, but I'm currently using the dedicated graphics. Perhaps it's allocating some of the RAM for the integrated GPU that's also in this machine.
Still got my old SSD with OSX on it for now sitting aside.
I used to use about 80-90GB on my OSX install. Now with all photos and documents on there (and I'm planning on sorting through the photos at one stage), the total amount of space on the SSD used is 36GB, including 25GB of photos/video.