memory upgrade

[Andrey84]

Sure, my own benchmark measurements on my i7 2020 iMac:

64GB RAM running at 2667 MHz: 8740 to 9029 multi-score Geekbench 5, memory transfer speed 28500 to 29600 MB/s Novabench.

64GB RAM running at 2133 MHz: 8240 multi-score Geekbench 5, memory transfer speed 24500 to 25660 MB/s Novabench.

Basically 6 to 9 percent drop in CPU multi-score (which I rounded up to 5 to 10 percent in my previous post), and 10 to 17 percent drop in RAM speed score.

These are only my personal tests, but I tried to be as fair as possible, I had no other apps running in the background, did it after rebooting and waiting several minutes. I was trying myself to figure out if dropping to 2133 made a significant impact.

Of course, real world performance is not same as benchmarks, but benchmarks are (almost) the only way we have to quantify comparisons.

Interpret how you wish

btw, OP can run their own Geekbench and Novabench comparisons if doubtful.

I would comment that running RAM with mismatched amounts in each channel (i.e., not full dual channel) results in even worse CPU multi-scores and RAM speed scores

Thanks for this. Yes, the difference in GeekBench is noticeable.
However, in the real world it’s had to say what it will be.
For memory transfer speed to become a bottleneck, I expect continuous loading of big volumes of new data, like video editing, rendering or benchmarks. I don’t see how normal system work and photo editing could be affected.
Thanks for mentioning the speed drop at the beginning in post #6. I guess we both missed it. You didn’t quantify the drop, and the comment wasn’t written like a warning, so we assumed an insignificant drop. Maybe it is.
Up to OP to keep 48GB @2133 or 32 GB @2667.

 

[thewall]

Update!!!

I have now moved the ram into different slots 2 X16gb into slots 1 & 2 and the 2 x 8gb into slots 3 & 4 and now the spec shows 48gb 2667mhz so happy days

 

[Andrey84]

Update!!!

I have now moved the ram into different slots 2 X16gb into slots 1 & 2 and the 2 x 8gb into slots 3 & 4 and now the spec shows 48gb 2667mhz so happy days

What might have happened is that you lost dual channel now, but gained higher transfer rate.
Apple's guidance clearly says that Channel A are slots 1 & 2 and Channel B are slots 3 & 4.

I'd install a memory benchmark (like PassMark), or even a generic benchmark such as Geekbench, and test this current config (1) 16,16,8,8 vs your previous config (2) 16,8,16,8 and also vs dual-channel 32GB (3): 16,0,16,0.

These configurations should all give progressively faster memory transfer speeds in MB/s. 2nd one gains dual-channel, which is more important than transfer rate. 3rd one has both, dual-channel and 2667 rate.

 

[Andrey84]

Update!!!

I have now moved the ram into different slots 2 X16gb into slots 1 & 2 and the 2 x 8gb into slots 3 & 4 and now the spec shows 48gb 2667mhz so happy days

Also I feel it's my fault this has happened to you - I didn't know the transfer speed would drop so much with non-matching RAM, but I said it's going to be OK.
I'm happy to transfer 50% of the cost of another 32GB matching pair to your PayPal account, so you can have 64GB of fully matching RAM, running dual-channel and on 2667Mhz.