It would seem to me that the CFM in an "opened up" system would be limited by the turbo inlet and the filter.. if your inlet is 2.5" (just a number out of the air, I have no clue what the correct one is), then it wouldn't seem to matter if you had a 2.5" or a 6" pipe between it and the filter. But, throw those curves in the pipe and it might change things some. Does a straight pipe have a higher cfm then one with a few decent mendrel bends in it? if so, then a 3" with the bends would seem to let you bring the pipe's cfm back in line with the 2.5 inlet.
But then again, maybe the filter is the true limiter here? depending on the flow of the filter, everything else could be moot.
LoL - I have no answers
When the UPS man delivers my OBD scanner/logger/dyno maybe I will be able to test all this.