New servers for MS Hyper-V

[BillClark22]

I'm looking at two different HP servers for a MS HyperV implementation.  My main concern/question of the proposed servers, are the processors. Server 1 is a ProLiant DL380 G7 with dual, 6-core Intel Xeon X5690 processors, with 72GB RAM/processor.  Server 2 is a ProLiant DL580 G7 with quad, 6-core Intel Xeon E7-4807 processors, with 32GB RAM/processor. 

We are replacing a VMware install that uses two, ProLiant DL360 G5's with dual, 4-core Intel Xeon E5335 processors, 32GB per server (not per CPU).  Right now the VMware hosts are under 50% of CPU usage, and around 70% of RAM usage with 20 VM's. 

I want capability for growth and ability to host beefier servers (Exchange 2007/2010 for example), but I don't want to overkill and spend $10k more than what I need.  So, what of the two proposed servers above would best fit the bill?  x2 6-core with higher clock, or x4 6-core with 1/2 the clock?  Any advice?  Thanks.

Bill