5 - Dell R610 with 96GB Memory in Each - Also has a 2 Port Intel 1000 Card (6 Nics Total)
What are you doing with 5 R610s that can't be done with two R720s? The memory count implies that the workload per node could be consolidated further.
If you're investing in mismatched EQL, why not look at 3PAR or HDS which have multi-node active/active symmetric access for their storage?