I attended CEDIA 2011 and asked the following questions of Spectracal CTO Derek Smith:
Buzz: Are there any hardware differences between the C6 and the D3?
Derek: No
Buzz: At 20% white I get 136 reads per minute with a D3 in ChromaPure and 30 something in CalMAN. Is the difference due to a slowing of the D3 in CalMAN?
Derek: Yes
Buzz: So the difference in price between the D3 and the C6 is read speed and the provided tables?
Derek: Yes
Buzz: Is a D3 profiled from an i1Pro more accurate for a given display than the tables provided with the C6?
Derek: Yes
The bottom line is that Spectracal is charging about double for less than the capability of which most of us already have.