Hello Tony,
Martin is not available right now and I'm taking care of the forum in the meantime.
Both processors are old server class/workstation processors. Hauptwerk likes "faster" clock speed, but to a limit. In the case of the 2643v3 -vs- 2673v4, while the 2643 has a faster clock speed it only has 6 cores (compare to 20), overall performance is less than half the 2673 performance. (benchmark of 17900 -vs- 36900!)
A simple, not exactly scientific, calculation to compare 2 processors (and I repeat, not scientific because other factors can impact the performances) is to multiply the cores x clock speed.
2643 = 6 x 3.4 = 20.4
2673 = 20 x 2.3 = 46 ...
Once again, more than double the value of the 2643.
I do wonder why you go with server class processor instead of an i7 or i9 12th generation processor who will provide similar and even more power for a lot less $ (less expensive proc, motherboard, memory....) My 2 cents...