Back in August I bought a base model 27" iMac out of desperation. It had the 1 TB fusion drive, which was awful. It would take close to a minute to open Outlook or Photos, and sometimes it would hang for no apparent reason, for several minutes at a time.
But ultimately it turned out to be a good decision, I think.
1. The base models are frequently discounted. I had Best Buy price match, giving me a $150 discount. Upgrade to an internal SSD and you will have no choice but to pay full price.
2. I ordered a 500 gb Samsung X5 external SSD from Amazon for $200. Now the computer feels every bit as fast as it should. I haven't bothered to velcro the unit to the back of my iMac...but I could.
3. I could have gone with a Mac mini, but there is no better monitor out there than the iMac's 5K display, not for under $5K. It is spectacular.
4. Now I have an extra 1 TB internal hard drive. I don't do anything with it yet...but I could.
I have only one issue with the computer, and that is that it doesn't appear to do memory swapping with the external boot disk. Sometimes my 8 gb fills up and the computer crashes, or it asks me to quit some applications. Someday I'll add another couple sticks of RAM, which is cheap and easy.