Mac Hardware setup for Lightroom

Your current setup is pretty close to as fast as you can get for Photoshop and Lightroom right now. Apple should be releasing follow-on Apple Silicon machines this summer/fall which would start replacing the higher-end iMacs. The iMac Pro is already discontinued. I would say stick with what you have for now.

my current bottle neck is saving changes

I can understand this in terms of Photoshop, but what does it mean for Lightroom Classic?

For Lightroom Classic:

In general, you want the fastest CPU you can afford. If you have a monitor that is 4K or larger, you want a high-end GPU as well. RAM above 16GB usually won't help Lightroom Classic, as memory is not a bottleneck. Put your catalog file on the fastest disk (usually a SSD) and it doesn't matter (beyond a trivial amount that you won't even notice) what speed the disk is that stores your photo.

For other software ... well I don't know, but you do know what software you have, and you'll have to judge if going beyond those statements for Lightroom Classic is needed.

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@Sanpanza wrote:

I have a rather large library and my current system setup is iMac Pro with 1TB SSD drive

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I don’t have any of that exact hardware since my Macs are different, although I do used a JBOD too (USB 3 at 10Gb/sec). but that iMac Pro is a good place to be in terms of Macs. The very fast iMac Pro internal storage should not be bottlenecking anything on it.

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@Sanpanza wrote:

I am thinking that I would buy an iMac (M1) 27" with 64MB of RAM

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No such iMac currently exists. The only iMac with the M1 processor right now is the base model 24". Its maximum RAM is 16GB. If you are looking at a current new 27" iMac with 64GB RAM, that is an Intel model. The Radeon Pro discrete graphics in your current iMac Pro might actually perform better than what is in the current low-end M1 iMac.

Because the current M1 Macs have replaced only the bottom of the Mac desktop and laptop lines, if you are looking for a large performance jump over your iMac Pro, my guess is that you are waiting for the next generation of Apple Silicon Macs that will replace at least the midrange and possibly the high end Macs too. Apple has not indicated how many months it will be before those arrive, but Apple has said they will transition all Macs to Apple Silicon within two years (of when the first M1 Macs were released).

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@Sanpanza wrote:

…and the same JBOD with updated  Lightning or USB 3 interface. 

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Mac hard drives are never attached by Lightning. Lightning is a connector for iOS (iPhone, iPad).

If your JBOD contains hard drives, if they are fast those max out at probably 150–200MB/sec, so they can be handled easily by the very common 5 Gb/sec USB 3 standard you might already be using, and upgrading the connection will not improve performance because the hard drives are the bottleneck.

If your JBOD contains SATA SSDs, those max out at around 500–600MB/sec. Upgrading from 5Gb/sec USB 3 to 10 Gb/sec USB 3 or 4 may improve things a little, but probably not noticeably.

If your JBOD contains NVMe SSDs, those can achieve from roughly 800 to over 3000MB/sec, comparable to the speed of Mac internal storage. The slower/cheaper kind should be connected through 10Gb/sec USB 3 or 4 to take full advantage of the SSD’s speed, while the faster/expensive kind (2000+MB/sec) should be connected by Thunderbolt, which is also expensive. These might improve editing performance if used as cache/scratch drives, but for editing photo files, a Thunderbolt connected NVMe SSD is unlikely to provide a benefit proportional to the high price, though backups and bulk transfers should go faster.

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@Sanpanza wrote:

…my current bottle neck is saving changes, image loading after ingesting into LR. Additionally my bottle neck in Photoshop is opening large layered files,  saving files, PS filters

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Saving changes: If from Photoshop and the files are on a hard drive in the JBOD, this might be improved by replacing the hard drive with an SSD. But Photoshop save speed can also be affected by everything from the specific file format to whether compression is on and that I think Photoshop saving is single-threaded (uses one core). So you may not be able to fix the problem completely by getting faster storage. I take advantage of Photoshop background saving, so if I hit Save I continue editing while it’s completing that save.

Image loading in Lightroom Classic: This is a function of how fast it can render raw to RGB, which is CPU+GPU. Storage speed is probably not the bottleneck.

Photoshop filters: CPU+GPU depending on how GPU-accelerated the filter is, storage speed is not the bottleneck.