This probably seems like a strange question so let me clarify. Obviously when you select the 6-core machine over the 4-core machine, you get more memory (16GB vs 12GB) and a GPU upgrade (D500 vs D300). This is NOT what I'm referring to. I'm referring to the actual architecture of the computer. For example, the 4-core machine uses the Intel 602J chipset. Do the 6, 8 and 12-core machines use the same chipset? Are there any tweaks to the cooling system, power supply, essentially anything not specifically specified by apple? The reason I ask is because the cost for a processor upgrade is significantly higher than the difference in price between the two processors. COST OVER DIFFERENCE IN PRICE FOR CPU UPGRADE: 4 to 6-Core: $211 4 to 8-Core: $571 4 to 12-Core: $1180 The above values are based on Intel's recommended customer tray price ($294, $583, $1723, $2614 for the 4,6,8 and 12-core respectively). The additional cost associated with each progressive CPU upgrade makes me wonder if something else is changing as well. If apple does use the exact same internal components regardless of CPU, you could save a bunch of money by doing the CPU upgrade yourself (right around the values given above assuming you sell the 4-core cpu). ifixit gives the nMP an 8/10 Repairability Score so this shouldn't be too difficult either.