Not quite identical. The 4,1 uses lidless processors and is much trickier to do a cpu swap. On a 5,1 it’s normal processors. So if I was going through all the trouble of piecing together a machine, I’d go for the 5,1.
I agree with you :I've done a few and installing some lidded CPUs is like a birthday party compared to a delidded install.
It's obvious that it's way more sensitive and needs some technical skills.
Another point is that
the OP @Teachermark01 started with a single CPU 4,1 .
I think the investment of a 5,1 dual tray and 5,1 backplane is more than double the value of the 4,1.
Whether this is worth it ,just to avoid the risk/trouble/challenge or whatever way we see it is up to him ...
Once the CPUs are correctly installed, the only difference that remains will be an SMC version number ...
Which I consider a cosmetic detail.
EDIT: perhaps selling the 4,1 + 5,1 dual tray = price for a DUAL 5,1...