I am really mixed on the E5 series. First off, they are absolutely great CPUs. On the other hand, they are really expensive. Some of the CPU tasks I have been running (will post updates soon) I'm seeing the dual E5-2690 show similar performance to a quad Opteron 6166HE system. Yikes! The performance is great, but it comes at a cost. Just to give you an idea, 100% load on both CPUs and I am pulling <400w with dual E5-2690's.
On the memory side, if you have 4x 4GB DIMMs per CPU, you will see 32GB in ESXi/ Linux/ Windows Server 2008 R2 and etc. You do not split the RAM.
Did you ever look at the AMD side? You could buy two eight core CPUs now, then upgrade them to 12/16 cores later. Also, the G34 platform still has one more CPU generation coming. CPU speed wise not comparable, but they are less expensive. Even two 2GHz+ eight core Opterons will be faster than the three SC1425.
Another thought is looking at the E5-2400 series. Likely you will see lower motherboard costs there because you have fewer DIMM channels to trace out.