Not sure, but could it be the case that your DAW cant make best use of so many cores ?
Eventually I would have chosen Xeon E5-1650 v4 CPU. I have the v3 version.
Passmark results are similar between 1650v4 and E5-2640: 14270 vs 15348.
But the 1650v4 is less expensive and has a much higher base clock and single thread performance.
My 1650v3 i.e. runs instantly with all cores at 3.6 GHz (100MHz more than base frequency).
So I could think of that a 1650v4 will run instantly at 3.7 GHz.
As I disabled CPU core parking (what Cubase btw also does if you enable their optimized energy profile),
my CPU will never be able to park cores which is a prerequisite to let (one or some) selected cores run at turbo speed.
Also the difference between base clock and turbo is with the E5-1650 v* much less (300 Mhz)
in my case with tuning even only 200MHz, as I run my system 100MHz higher than base clock instantly.
The E5-2640 has a base clock of only 2.4 GHz and I think it can only really unleash its full potential,
when all the cores become really utilized.
So to sum up, I have a certain suspicion, that this CPU which also has a much lesser TDP of 90W,
potentially is for certain applications not so powerful.
Also take into consideration, that instant changes of CPU frequency also cause kind of lag, as
the CPU needs - as far as I know / heard - also some time until the new clock frequency is stable.
Thats I think the reason why many tunings for audio bring the CPU to a fix clock speed, which
also brings lower LatencyMon values.
EDIT: So having all cores constantly running at a higher base speed I personally regard as an advantage
over a design where you have many cores at much lower speed, where you eventually would NEED
turbo speed but then might get latencies by frequent CPU frequency changes.
If your system is still new, I would eventually a change of CPU also take into consideration.
Its might be a nice server CPU for virtualization, but potentially not for DAW work.
For this topic sadly you do not find much information in the internet.
So much is based on guesswork and own experience from the datacenter
where i.e. an Oracle DB benefit from an AMD Opteron system with less cores but higher clock speeds compared to a SPARC system with many cores but lesser clock speed.
Sorry, many suspicions from my side, maybe somebody else with a system with many cores at lower clock speeds can comment to this.
BTW what DAW are you using ?
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13