Switching CPU tray from Mac Pro 2010 to Mac Pro 2012

From what I've heard you can switch between 2010-2012 without any changes.

 

If BOTH machines are authentic 5,1 (not flashed/hacked/upgraded from another model to ID as 5,1) then YES - the tray from 2010 will work in 2012.

If you can still use your 2010 with this 12-core tray, check System Information > Hardware for SMC version. It should be 1.39f11 to work with the 2012. They SHOULD be the same for system and processor tray and SHOULD be the same between 2010 and 2012. Another SMC version number would likely indicate a 4,1 tray part.

As for RAM, you can max out a 12-core at 128GB. Currently running a 2012 Mac Pro 5,1 (that was upgraded from a 6-core original part) with a 12-core dual 3.46GHz and 128GB RAM via eight 16GB 1333MHz DDR3 ECC DIMMs.

As for the best RAM setup, I find it's debatable. Scoring from machine bench tests typically say to use less RAM (6x16GB=96GB) for best performance, but I'm often using beyond 96GB with Adobe After Effects CC2018. If your applications are not using beyond 96GB, then there is a debate if it's useful to max out or not.