Well, I asked a question about this on Mac Pro FB page and they told me that Mac Pro can last long.
I could go either way here. If it isnt broken then don't try to fix it or get rid while it is worth something.
If you really prefer the Mac Pro desktop and don't use the MacBook Pro, then sell the MacBook Pro while it is worth something. However....
What do you do on the mac Pro that needs the Mac Pro performance? editing photos doesnt need a pimped out Mac Pro. If you are concerned about cooling, then something may be wrong. Short of mining bitcoins or heavy extended periods of intense number crunching, your machine should not cause concerns for cooling. Keep an eye on that.
I did a quick search on Geekbench (I know not conclusive but hey just a quick check).
2010 Mac Pro is typically scoring around 3,050 for single thread and 14,785 for multithread. A 2013 MBP 2.4Ghz scores 4,058 single and 12,753 so marginally slower on multi-thread tasks. A 2017 iMac scores 5,279 single and a whopping 17,158 multi-thread. It is a significant performance jump over the venerable mac pro and they support multiple monitors.
Now, here's the thing, If you keep the Mac pro now, Mojave may be the last OS upgrade to support it. Two things I would consider there. First, it has life left in it yet but, after Mojave, it's resale value will plummet because no one will want to buy unsupported hardware at a premium price especially not hardware vulnerable to the likes of the chipset level security flaws we have seen of late.
I think you need to be thinking whats next in your refresh plan and selling the Pro to keep the MBP might actually make more sense. You can use the MBP with multiple monitors and a docking station so it wil be exactly the same as the desktop experience yet in a pinch you can grab and go.
This is just the ramblings of a mad man but hope it helps.