Here the textfile with my system configuration and some further backgrounds:

First my Mac configuration:

  Model Identifier: MacPro5,1
  Processor type: 6-core Intel Xeon
  Processor speed: 3.46 GHz
  Number of processors: 2
  Storage: 96 GB
  Boot ROM: 144.0.0.0.0
  SMC: 1.39f5
  GPU: NVIDIA GeForce GTX 680 (with Apple EFI boot screen)
  3 x monitor: DVI1: 24 "1920x1200, DVI2: 24" 1920x1200, HDMI: Sony-TV 1920x1080

The following boot systems:

SATA Bay 1 => SSD 480GB:
- Mojave (APFS with Preboot & Recovery) => My main system

SATA Bay 4 => SSD 128GB:
- EFI with OC + Catalina (APFS with Preboot & Recovery) => my catalina test system

Dual SSD PCI module: SSD 1TB with the following additional system partitions
- Sierra (HFS +)
- High Sierra (HFS +)
- Recovery 10.13.6 (Apple_Boot)
- Mojave (APFS container with Preboot & Recovery) => little mojave test system

Until recently, my work system was actually still a high sierra. For the switch to Mojave, i took my time until software upgrades from both Apple and 3rd party applications, which were then no longer HS-compatible, ultimately forced me to do so.

Hence my reason to deal with Catalina early on:
I would definitely like to be prepared if Apple discontinues support for Mojave in 2021 and my Mac is no longer supported by Apple.
I had the topic similarly years ago with my MP2.1, which i initially continued to use with chameleon bootloader, later with Pike's EFI patch, up to El Capitan ...

About Catalina: Sure, of course i also dealt with Dosdude's solution.
But what bothers me here is the handling of software updates that can only be installed patched again. On the other hand the "Vanilla" variant with OC is much smarter.

So it is not about upgrading to a not yet fully developed macOs in the blink of an eye, but rather treading a path that will make it easy for me to switch finally in maybe a year, because i will then hopefully know how it works best for me. 
Staying on Mojave is not an option, since the programs i mainly use, especially Apple-Software, will only become supporting Catalina in later updates. Many other Mac users will run into the same problem and don't want to stuck on not updatable paid dearly applications