I am mining with:
1. Dell Poweredge C6100 server I got from eBay with 4 nodes and two 4 core Intel Xeon L5420 CPUs per node. Hash rate per node=~70 Kh/s
Here is the cpubenchmark.com comparison for the Dual Xeon L5420 compared to other CPUs: https://cpubenchmark.net/cpu.php?cpu=Intel+Xeon+L5420+%40+2.50GHz&id=1259&cpuCount=2
2. Dell Poweredge C6105 server (eBay) with 3 Nodes, and two 6 core AMD Opteron 2419EE (North Bridge) variety. Hash rate per node=~77Kh/s
Here is the cpubenchmark.com comparison for the Dual AMD Opteron 2419EE compared to other CPUs: http://www.cpubenchmark.net/cpu.php?cpu=AMD+Opteron+2419&id=1858&cpuCount=2
You have probably seen me on nonce-pool hashing under the same moniker I use here. Current hash rate for these two servers is 524.07kH/s combined.
One server draws at max load about 450 watts for 4 nodes. For 3 nodes it will be less than 450 watts.
I was previously mining ducknote with these, here is the YouTube video I made: http://youtu.be/zmvVZMRcvFE
Counter-intuitively, the AMD Opteron CPU is cheaper but hashes quicker on M7M algo.
The more expensive Xeon CPU will hash quicker on cryptonight algorithm than the Opteron CPU (as expected).
JoeLao the 3-node Dell Poweredge C6105 is dirt cheap looks junky on the outside (refurbished of course) but it works good, if you need a spare development server.
Here is the eBay link they still have a ton of these (48GB RAM total, so 16GB Ram/node, comes with 3 250GB HD one for each node):
http://www.ebay.com/itm/DELL-C6105-CLOUD-SERVER-6x-1-8GHz-AMD-6-CORE-48GB-RAM-3x-250GB-C6100-SERIES-/171187983886?pt=COMP_EN_Servers&hash=item27db99560e