so I just upgrade one of the RAM slots in my mid-2012 MacBook Pro A1278, and even though people say it's not "optimal" to have different sized RAM cartridges in the slots, I'm here with empirical data proving the contrary. My MBP is LIGHTNING now, and EXPONENTIALLY faster than it was at 4gb of RAM. Running macOS Sierra is like a dream! Question: Now that I have enough RAM, should I upgrade to Mojave or Catalina or stay on Sierra? I would think if it ain't broke, don't fix it (i.e. stay on Sierra), but I'm open to educated opinions and quality feedback 