OP:
I too recently upgraded to a 2019 iMac, only i did it from a 2008 iMac that had been upgraded to 6g Ram and a 250g SSD years ago. There was (is) not really anything wrong with my '08, and it was still extremely snappy for day to day use. The SSD made this possible. BUT, the Photos app was becoming a wreck to try and use. It took forever to open, forever to do anything, and I hadn't been able to import pictures from an iPhone without doing work-arounds for the last few years since Sierra was the last OS I was able to put on it. New file formats and app updates, etc. were slowly making the old machine less useful. And I knew more of the same was coming down the road with the next OS update.
My wife getting an iPhone XS was the last straw for me. I almost lost 4 years of her pictures, managing to pare the loss down to 4 months by digging through Time Machine to find an old iPhone backup up that saved (most of) the day. But I digress.
So I bit the bullet and bought a new iMac. Top tier 2019, 8g ram, 580x 8g Radeon. Upgraded to 512 SSD because I knew the Fusion drive was likely going to feel slower than even my '08, as I had played with various iMac in the stores over the years. I've kept my data on external drives for years anyway, and don't really need 512g, but now I've got room to grow.
Frankly, I am also disappointed by the performance of USB3 vs the FW800 I was using on the "08. Faster yes, but not shockingly so.
Here's the difference: Photos just works, and it's pretty fast. even with an external library. Every wait I have is limited to the lazy write and read times of that USB3 external. I'm considering an external 1TB SSD, but I think upgrading my RAM would be of better value, even though for most tasks the 8g seems just fine, even with 5 different potential family users logged into the machine.
And the BIGGEST difference?: Encoding a DVD rip in Handbrake used to take me about 2 hours. This new machine does it in 15 minutes.
15 minutes! Do I need it to do it that fast? Not really. But now I don't worry too much about having to wait overnight for something to finish.
And 5K Retina is makes photos editing so much better. Not to mention my daughter loves being able to play Sims 4 with everything set to High, and the machine doesn't break a sweat.
Long story short? SSD. I can't wait until 4TB SSD's are the norm and we can all dump these slow ass HDD's forever. It's a travesty that any iMac, which is supposed to be a luxury machine, comes with anything other than an SSD.
