@danj Hey Dan, I'm late to this comment section but hoping you see this! Really wish I read some of this before purchasing my computer because I unfortunately purchased the Fusion Drive.
I now am in the process of upgrading my iMac to the max I possibly can and have decent money to spend. I have already upgrade to 64gb RAM (really easy obviously) and was getting ready to upgrade to i7 processor as well as a second internal hard drive. I watched a video on youtube of a guy who did this, but realized he also said at the beginning he bought the version with the SSD and not the Fusion Drive.
So being that I have the Fusion Drive version, and I hypothetically want a second internal hard drive, could I replace my current Fusion Drive with an internal SSD as well as adding a second SSD hard drive, the Crucial 2tb one was the one mentioned in the video and I was getting ready to purchase.
I appreciate your help, thanks!