John Kranz wrote:
Okay. I've decided to bite the bullet and put an end to this debate that 'something must be wrong with your computer" or "your Mac is too old."
... -- do you recommend I get a firewire cable and transfer everything over from my Mac that is being brought to a halt since my update to CAPITAN?
But is that the right thing to do?
No one can possibly answer that question for you John because you, like 99.99% of everyone complaining El Cap ruined their Macs, steadfastly refuses to post their own Discussion containing specific information about their unique installation that might help reveal what's wrong with it. All you have said is that you are "in the same boat as some others" which conveys no actionable information.
Post your own Discussion, and some guidance might be possible. Without that information, it's not.
The new Mini has no FireWire port, but you could use a FireWire to Thunderbolt adapter, or connect the two Macs over your local network.
I don't recommend using Setup Assistant because it's extremely likely that your existing Mac is running software incompatible with El Cap, or is simply ill-conceived garbage that should not be installed on any Mac of any age new or old, but that is complete and total speculation — because you haven't provided any details in a Discussion that you created.
Please read Writing an effective Apple Support Communities question.