This is only my two cents, but here it goes.
Unfortunately, it’s been about a nearly two years since I've experimented with multiple windows servers interacting with one another. I only have the need for 1 Windows server. I experimented with 2012 bata about a year ago and finally just switched to it on a permanent bases about a month ago. I'm still very new to server 2012. I played with hyper V extensively under 2008 R2. While it is very simple to use, I am now disappointed in the product after the discovery and understanding of VM ware. Under server 2011E, I was using vmware server for virtualization since it did not contain hyper v which turned me on to vmware in the first place. VM ware server works well but always felt piecemealed to me. It lacked the refined nature of Hyper-V. I use shy away from ESXi since I didn't have a processor that supported VT-d. That is no longer an issue for me and after playing extensively with ESXI, I'm a fan!
ESXI is different from the standpoint that it requires software installed on a client to connect to. It is very different from windows, so expect a bit of a learning curve. It is Linux at its base. Therefore, if you want to make tweaks like getting ESXI to shut down from the command of a UPS or other more complex tasks, expect to do some SSH and command line. I definitely used a few how to articles to get started. After a couple weeks with it, I started to see it as highly refined, extremely powerful and highly adaptive for my needs. I've been running ESXI for 8 months now and can no longer see a close second in terms of capability.
My next wish is to find a cloud solution. I was playing with Xen but found it clunky compared to ESXi. My intent with a cloud is to use very light weight, low power server such as an E3-1200v3 for an always on router and server all in one solution but still have the capability to power up other nodes to give me the horse power and RAM when I need it. I also want the light weight server to have a small storage pool that gets backed up by the larger server and again to a off sight server. The light weight server will host the client PC's iSCSI boot drives to consolidate SSDs into one extremely fast array and reduce number of drives required. Ideally, Server 2012 will move over to the large server when its booted up and back to the low power server during times of low usage.
The point I'm attempting to relay to you is, if you want low power, look to removing as many devices as possible. Today’s hardware is significantly under utilized by today’s software. Therefore, try to consolidate as many physical PCs into one as practical. This isn't always possible and without understanding your needs and intent, hard to make recommendations. However, if you look to big business, they are vitalizing for the same reasons. Hardware is plenty fast for 90% of the functions any one server is going to accomplish. You can save money on hardware and power by vitalizing.
Your C6100 is extremely powerful, even with the relatively slow L5520s. But there are two of them which give it many threads to accomplish multiple tasks across multiple virtual machines. If you do have a task that requires higher clock speeds, maybe an upgrade to an L5539 or better is the right move for you. If you are a home user and not doing anything extreme, I wouldn't waste money on multiple separate servers which multiply the amount of power required.
While I'm still in the experimental stage, I'm finding that the C6100 with L5520s is all the horse power I require to serve my house, lab, and file backups for a couple businesses all at 10Gb/s speeds. I am not doing any databases which would likely change this assessment to a degree. I would argue that this is the case for most of us home users. My only complaint with the 6100 is the lack of expansion slots for my custom solution. It makes for a wonderful lab, just with the requirement of more devices. If you have the need for speed and constant experimentation with the funds to buy more servers, well, who am I to judge (guilty with the 6100...). I prefer to spend my money on 10GB cards (possibly infiniband in the near future), fast switches, network KVMs, UPS with network card that shuts down my network after backup is complete for the night to save power, the constant problem of not enough HDD space, etc. All my experimentation is leading up to building one expensive server that reduces as many devices as possible across my network and does so efficiently.
For an always on PC, the 6100 is not ideal to me. It is power hungry, especially with multiple nodes up! But for a lab, you can't beat it.
I again ask, what is this going to be utilized for?
