AFAIK it's normal for ECC Ram to be slightly slower.... if... the ECC is also activated in the BIOS.
Otherwise, I presume it should be the same as normal Ram.
In my case, there was no difference in SpeedSys between a single-sided and a dual-sided module of the same size & speed.
Today, I also installed a K6/2+ @550 on this board; and compared with a picture of SpeedSys that I have of the first board with a K6/2+ @550.
And except for the CPU score being a few points slower (on this board); all other numbers are virtually the same.
I will try to continue some RAM experimenting & benchmarking in Windows; as I have installed George's Memory Interleave Enabler for VIA Chipsets (https://www.georgebreese.com/net/software/) on the previous board, and the RAM speed was noticeably higher.
But I never got around to testing single-module vs multi-modules. Or single-sided vs dual-sided.