I agree and I considered those options.
When it came to RAM my search yielded over 3,000 choices! The brand of RAM is largely irrelevant compared to the boost of increasing from 4 to 16 GB total memory. RAM is a commodity in that most brands don’t actually manufacture their own parts. It’s literally just a sticker they attach and the maker can vary from month to month.
I didn’t do a simple SSD swap on the main hard drive for cost reasons. The stock iMac spinning drive is 1TB which would cost $440 to replace with a Samsung 850 Pro SSD. The 120GB SSD that holds my OS and apps was just $92. I couldn’t recommend putting in a drive that cost more than the computer itself but that’s fine if money is no object. I’ve done it myself on some backup machines.
I’ve had no heat issues. There’s a fan control app that I installed (but forgot to mention) that corrects for the lack of a heat sensor on the SSD.
I didn’t know about the different data speeds between the HDD and optical drive connectors. That’s good info. The speed boost from HDD to SSD was so dramatic that I could appreciate that. Thanks for explaining that!