Gary,
May I
chip in on this?
In addition to what you said:
E5-2620 is the first "sweet spot" with 6 cores, 15MB cache and 1333MHz memory access, at $406 (Intel tray price). Models lower in line have 1066MHz (30% slower)) memory bandwidth, 10MB cache, 4 cores, i.e. this is a significant jump.
The next one is E5-2650: 8 cores, 20MB cache, 1600MHz memory bandwidth, $1107.
A Dell T5600 or my favorite, T7600, will cost about $4K+ with dual E5-2620s, nicely configured. With dual E5-2650s - $7K+.
HTH.
Alex Gerulaitis
Systems Integrator
DV411 - Los Angeles, CA