They do not
All CPU architectures out there when running flat out (as a well spec-ed server farm generally does) have very little advantages over each other. The rumors of Power being err more powerful (pun intended), arm consuming less power, etc end up being very exaggerated.
Arm's "less power" comes to play when it is idle. Same MIPS at full flat out Intel will use times more power in idle. That is a mode of operation which you will see in consumer equipment, media boxes, house server, etc. You will not see it in most datacenters nowdays. VMs, Cloud and Big Data have changed the way they are run. 10 years ago, servers were run at a fraction of their capacity to ensure they have enough spare grunt to handle incoming requests. Now they are run in an almost mainframe fashion where there is a low priority VM set with a batch processing job always crunching something in the background.