The Pi's will be using those 200Watts at near full tilt. The main use here would be larger computational tasks that you can easily split up among the blades. Or you run a very hardware-failure tolerant software service on top.
Hrm, interesting to see how the TDP of those 8358s drives overall power consumption. I'm looking at the idrac consoles of a couple R720XDs with 12 3.5" hdds, >128gb ram, two E5-2665s per, and they're all currently sipping ~150W at < 1 load average. The E5s have a TDP of 115W to the 8358's 250W, so I assume that's what's most of it. I admittedly do some special IPMI fan stuff, but that only shaves off tens of watts.
Umm, I'm not sure I can afford the electricity to run kit like that :)
I'm currently awaiting delivery of an Asus PN41 (w/ Celeron N5100) to use as yet another home server, after a recommendation from a friend. Be interesting to see how much it draws at idle!
Q: Why would a 1U server need more than 200W if you're doing nothing more than basic network services?
I have mini tower servers that draw a fraction of that at idle.