If your using high iso and f2.8 zoom lenses then best stick with full frame. But if using primes only like myself then a different story.
More a zoom guy so rarely going below 2.8... occasionally put on the primes, but more 70-200 or 28-70
Im shooting on olympus using leica glass. Its micro four thirds so double crop factor. Only downside is high iso. But because i can shoot fully wide open at f1.2 i don't need to increase the iso. For years i was always full frame but could never use lenses wide open. Trying to use 1.2 canon L glass comes out soft and impossible to nail focus with to much shallow depth of field. Rule of thirds was impossible for weddings Which makes it useless for me and pointless. The pro with micro four thirds is that everything is very small from body to lenses. And because of the double crop depth of field isnt as shallow so it can focus very quickly but let in lots of light. E.g, an f1.2 lens gives depth of field of 2.4 but lets in the light of 1.2. But depends on how you shoot, your style. I only use primes.
What are you shooting on? I have so much canon kit that not sure I can make the transition... And seen some amazing shots on ridiculously high ISO on the 5d4. How does yours compare?
I have an 80d with 5 lenses, worth the upgrade.