I was running my iMac on a T3 for a while and it was just as fast (if not faster) then the internal Fusion drive.
Just so folks don't get confused when reading this thread, the Samsung T3 would appear to be just as fast as Apple's Fusion Drive on a regular iMac, but for the sake of this discussion, we're comparing it to the ultra-fast SSD in the iMac Pro.
If I have a new iMac Pro base model, and use a 2TB Samsung T5 external SSD as my hard drive, I won't notice much of a difference in performance, would I? My goal is to be able to unplug it at the end of the day and take it with me, so others can use the computer and I can work on my things at home on my MBPro.
The T5 has a pretty fast read write speed (one of the fastest from what it seems after some online searching) so there would be virtually no downside as far as performance for using the external SSD as my hard drive, would there? It connects by USB-C, so...?
Just double checking before I order the Samsung T5. Thanks!
In order to answer your question of whether or not the T5 is fast enough, we need to know what your needs are.
Before we get started with that, I am assuming you are talking about storing your data on the Samsung T5 and not booting the iMac Pro from the Samsung T5. If you do prefer to boot from an external drive, keep in mind that you will lose many of the security features from the iMac Pro's T2 chip.
Back to using the Samsung T5 to storing your data, if you are simply doing everyday office/life work, then you will not notice any slowdown at all. If you are simply accessing photo projects and doing normal editing, you will not notice any slowdown. If you are editing single-stream 4K video, you will not notice any slowdown. However, if you are editing intensive multi-cam 4K video, then you might start to see a bottleneck. Of course, there are many more usage applications than just photo and video work, but I use that as a reference since that is the large majority of my work. So back to the original question: what are your usage needs? Let us know and we can get you a solid answer.
As for me, the projects I'm actively working on in my editing suite are stored on my iMac Pro's internal 4TB SSD drive. This gives me ultra-fast unfettered access. Then when I'm finished with the job or the task at hand, I send that data over to an external Thunderbolt 3 RAID 5 array. I also travel a lot (about 130-140 days a year) so I have a couple of 2TB Sandisk Extreme Portable SSDs that I use in the field in conjunction with my MBP. Then when I get back home, I simply plug them into my iMac Pro and resume my work. The Sandisk Extreme Portable SSDs are faster than the Samsung T5 and are cheaper if you catch them on sale. They are slightly larger than the Samsung T5 though, but not by much. Anyway, I thought I would mention the Sandisk to you since you're in the market for a very fast, small portable SSD drive.
Bottom line: small portable SSD drives can be a great way to bounce your work between a desktop machine and a laptop, but as far as "will it be slower", it all depends on the work you're doing.
Edit: After posting this, I happened to check B&H Photo and discovered that the 2TB Sandisk Extreme Portable SSD is on a super sale for $379, but only until Nov 3. This is significantly cheaper than the Samsung T5. The Sandisk is well regarded and loved by many. Mine have been great. And good grief, this is a great price!
https://www.bhphotovideo.com/c/prod...sk_sdssde60_2t00_g25_extreme_600_2tb_ssd.html