New 12-core Mac Pro, starting at $3799
apple.com
apple.com
CPU: $260, 3x2GB ECC DDR3: $60, 1TB 7200 RPM HDD: $120, Radeon HD 5770: $120
six cores nehalem start around 1000$ according to wikipedia
http://en.wikipedia.org/wiki/Nehalem_(microarchitecture)#Ser...
While probably far from "best bang for the buck", the 2 2.4GHz is probably closer to the real cost than the other models.
Best 6 cores for the buck seems to be this baby right now, although it doesn't seem to support multiple processors as it is not a Xeon DP. http://ark.intel.com/products/63697
Apple doesn't generally hold events or give keynote time over to simple spec bumps in product lines that aren't hugely popular, like the Mac Pros, or the Mac Minis.