Downgrading processors in R640/R740

We have an R740 happily running with a couple of Xeon Silver 4114 CPUs and plenty of RAM and disk and most importantly, a GPU. Recently I picked up a working, second hand R640 with a pair of fancy Xeon Gold CPUs. Yesterday I tried swapping the CPUs over so that I could have the better CPUs in the bigger box that can accommodate the GPU. Moving the Gold CPUs into the R740 worked flawlessly but when I put the Silver CPUs back into the R640 it refused to recognize the RAM and claimed that there were no DIMMs installed. I’ve swapped the processors back and it all works just fine in the original configuration, which suggests that I didn’t just break something, but I’d rather understand the issue before I do any more movement of expensive, fragile CPUs.

Looking through all of the settings that I can find, it seems that the R640 RAM speed is set to 2999MHz, but the fastest that the Xeon Silver can handle is 2400MHz. Try as I might, I can’t find a way to change this. I tried creating a new, custom System Profile and set a slower speed in there, but got the same problem.

So my question is: is there a way to set *all* the BIOS system settings to the defaults that Dell would have used if it had shipped the R640 with the Silver CPUs? If so then hopefully it will work with the swapped CPUs. If such a mechanism exists it might also be handy to do the reverse and reset the motherboard settings on the R740 to the defaults for the Gold CPUs.