First things first, EB's 6. 7 is not a 07. 5 6. 7, and is a lot more reliable, and has the Aisin automatic, it is an 07MY C&C bought in 06. There is no such thing as a 07. 5 C&C. There are some differences between his and mine, that was built in Feb 07, (look at sig) the cosmetic cover over the EGR bypass tube and the EB was not included with the engine, but could be turned on for a fee. But overall the engine is the same as mine and the C&C's have a different emissions setup. The C&C's are also rated at 305HP unlike the 07. 5 6. 7/46rfe with the 350HP. The C&C's did not meet the 2010 emissions in 07 like the 07. 5 6. 7 did.
I would not buy a used 07. 5 6. 7 unless the emissions have a warranty that has at least a one year 12K mile (1/12) warranty included with the truck. There were many buybacks and many problems associated with the early 6. 7's except for the C&C 6. 7, that had different emissions controls. The potential of the truck the OP is looking at, can be a good truck, but a Carfax needs to be ordered on it, to see what/if it had emission issues or was a buy back truck. As Bob4x4 states, they have a higher risk than the 5. 9, but a newer model from 09 and on, has a better chance of emission free issues.
The 6. 7 with the 46rfe Auto is a good combination rather than the 6. 7/G56, it pains me to say that, but the history on the the 46rfe has been good and has done well with the 350HP. Mine with the C&C 6. 7/G56, has had an issue, but not until after the ECM was updated. It was my fault though, I was given the choice on the update, if I wanted the new update in 09. I now have surging issues when in regen when rowing through the gears and it has taken out my clutch. Its now going to cost me a couple grand to beef up the clutch and trany to counter the regen and surging issues when shifting at RPM's higher than 1900 RPM.