I have a question regarding relative 'strength' of adventures.
Would a 6th level DCC (d20) be suitable for 6th level C&C characters?
Sorry for not noticing the question & it seems no one else answered either.
I think a DCC module, as run, would work within the levels listed. However, when a 3.X module assumes the PCs will advance one or more levels during the adventure, then you need to reconsider the levels your PCs are.
An example is Necromancer's "Fane of the Witch King." The posted levels are 4 to 6 and the party will level up to 10th. A party of C&C characters, levels 4-6, will almost surely die in this module. The power of the villians ramps up, but the PCs won't in time. In this case I'd recommend uping the PCs levels to 6-9. Early encounters may be somewhat of a pushover, but the later ones will still be very deadly.