Due to limited funds I bought the base level MacBook Air with ‘only’ 8GB memory and have been very pleased by its performance compared with my old 8GB iMac for basic office productivity (including large Excel files and running Python scripts).
Now I’m due to replace my ageing iMac I’m similarly unable to afford the 16 GB version.
Will performance in the 24" iMac be almost identical? Or does the iMac take resources to run the big screen? Any experiences?
Thanks
Given the fact that MacBook Airs are fine running external displays up to 6K, I would expect that the M1 iMac should not feel different in comparison to your MacBook Air. I might be wrong, but I think that the number of GPU cores is more important than the amount of RAM when it comes down running a “big screen”.
Maybe, there is somebody here who is able to share her/his first hand experience of both the M1 iMac and the M1 MB Air in comparison to each other.
P.S. Try to get a refurbished M1 iMac when it is available. The refurbished store always is a good option. 
+1 for Apple’s refurb shop. I picked up an M1 Mac Mini with 16GB of Memory and a 256GB SSD for cheaper than normal, otherwise I wouldn’t have been able to stretch to the 16GB.
NOTE: Be aware that the base model M1 iMac does not have touch ID. (At least the model my Dad bought does not have it.)
Thanks. My ‘affordability’ is in terms of second hand prices as tbh these days I am happy buying second hand off Ebay as computers tend not to go wrong. And most M1s will be under warranty.
I did some (rough) checking into your original question, and I think you should expect about 10-20% more memory use from WindowServer on the 24" iMac over the 2020 MBA. Of course, this depends on how similar your open windows are on both computers.
As far as speed, the iMac will run faster than the 8GB MBA since it has one more GPU core, and the CPU isn’t passively cooled.
Overall, I think that if you’re happy with the 8GB performance on the MBA, you should be happy with the 8GB iMac, but since it’s going to use up to a few hundred MB more RAM, it might be worth looking a little harder for a deal on a 16GB. I also agree you’d want the iMac model with more ports and Touch ID if you can find a reasonably priced one. Good luck!