I understand you are looking for processor upgrade compatibility information.
Please bear in mind this type of information is handled by your server manufacturer. You need to contact your computer manufacturer for more information about this matter.
According to server specifications (Dell PowerEdge R820), the server comes with an Intel server chipset C602, the link below shows a list of possible compatible processors for Chipset model C602:
See compatible products link on the left hand panel:
For more information about R910, you need to check with Dell as it appears to be a customized chipset for your computer manufacturer.
Many thanks Allan for the help,
Am I correct if I say that the R820 with E5 is much more powerful than the R910 with E7?