Its listed in the service manual
30" primary @ 1.75 is a very good primary size/length for the stock motor. The diameter targets a peak torque boost right around 4600 RPM, and the length targets about 3900, a good point that helps extend the upper power band, coincidentally the CES exhaust is very close to these numbers.
The collector and post collector length will pivot the curve around that 4600 number, so shorter will tilt to to increase upper/decrease lower and vice versa. Paul's systems look like they will, guessing here, target something like 4800/5000 for peak pulse tune, also a very good spot, I expect they make power graphs similar to CES.
Carps pipes do indeed have bigger primaries, moving power up to 5900, shorter primaries, moving power up, BUT, they use the megaphone collector style that's fairly long, this will increase exhaust gas velocity, improving bottom end, so it will make a good "everywhere" power curve. What you will find, is as exhaust flow increases, primary diameter will matter more, so yes, on the built motors the non-carp exhuasts using 1.75 "may" cause a reduction in ultimate top end power, but should be trading that off for an increased area under the curve, BUT, if 1.75 just becomes straight up undersized, they would lead to a reduction everywhere in the RPM band vs the 2.0 primaries.
I should qualify that I am of the opinion the Carp pipes will make notably less power at part throttle conditions than any other R3 system out there.
If you look at cam timing, it creates peak power low down, so having the exhaust create power higher up extends the torque curve giving a longer, broader power band, something reflected in all the dyno graphs of aftermarket headers (besides zard's garbage).
Someday when my **** dealer gets off their asses and gets my 265 head/cams put on, we'll find out, I plan on going sidewinder at some point, so there can be a back to back apples to apples ces vs carp header on the 2wdw dyno when I get to WA.
