Originally Posted by MichaelB
Sorry I haven't been back to the thread - it's lack of time, not interest. The positive responses are encouraging, I think I'll install this one.
This is always one of my two top concerns. Newer SW versions mean more functionality, but this demands more system resource. Soon enough, the hw isn't sufficient and the system slows to the point of annoyance or even no longer usable.
I haven't noticed any slowdown with Sierra at all.
What is missing are features that require new hardware. For example, there are a number of features that use newer Bluetooth than my old iMac supports. So a number of the "continuity" features aren't available on the iMac. No handoff, universal clipboard, auto unlock (using the watch), and so on. (https://support.apple.com/en-us/HT204681
Another example is that older Macs with older GPUs (the chips that accelerate graphics) simply can't do certain things. So the old iMac doesn't have as many photo filters available in the Photos app.
Now if you have a small amount of RAM (maybe less than 8GB, certainly less than 4GB) I'd recommend more. My 6 year old iMac has 12GB so I'm good.
Oh, and anyone who's running on mechanical hard disks. Well. The difference is HUGE.