I have a 2019 27" 5K iMac on my desk at work, and I just upgraded to a baseline iMac Pro 8 core for home to replace my aging nMP. I got the iMac Pro refurbished from iPowerresale for $3500 - it came with the 1 year apple warranty too. Here's the link:
https://ipowerresale.com/product/27-imac-pro-8-core-3-2-5k-late-2017-space-gray-2/
A quick, subjective comparison of the two machines:
Sound.
Winner: iMac Pro. Quieter at idle, far quieter at load, and far better speakers. I hate computer noise, and the iMac Pro is the quietest computer I've ever owned. It's amazing.
Speed.
Tie. The 2019 5K iMac "feels" snappier during day-to day use. The iMac Pro is actually massively faster when loaded down with virtual machines, running simulations, autocad, etc. And did I mention it's almost silent under full load?
In the past I had a 5K 2014 machine, but I sold it off in ~2016 for an nMP because the iMac was too slow for my work. As other commenters have said, it ultimately depends what you need your machine to do for you, but you will know if you
need an iMac Pro. If you don't need the power but you're willing to spend the extra money over the regular iMac then go ahead!
I think either option, a regular iMac 2019 or an iMac Pro, would be a massive improvement for you over the 2014 iMac, but given what you've said I recommend the regular iMac (with SSD!!!!). With the cost savings you can hold onto the extra $2000 and buy another iMac 5K in 5 years when the iMac starts to slow down. Or you can run your existing iMac for another couple of years and then jump in on that sweet 2024 iMac. I hear they're going to be awesome.