Have you calculated the effective caliper piston area on a 2004-2007 CTS-V 4-piston caliper, it's about 3.6 square inches IIRC, very comparable to a C4 twin-38mm piston caliper, albeit with a staggered 40.5/36.5mm piston diameter design.
The effective piston area of the C6 (twin 40.5mm) and C6 Z06 calipers (33mm) is about 10% larger at 4.0 square inches, so in the case of the C6 Z06 where both would be using 355mm rotors and assuming the same CoF pads, MC bore size, etc, should produce 10% more brake torque for any given pedal effort. You'd offset some of that by stepping down to either the 340mm C6 Z51 or 325mm C6 rotors, but it sounds like you're considering doing the same with the CTS-V calipers as well.
I'm probably biased, but if you're only increasing your track usage, then I would suggest that you go with the largest rotor and caliper combo you can fit inside your wheel and still afford. The simplest would be a C6 or C6 Z51 type of kit. The CTS-V calipers use a pad with a very tall radial height (~60mm) and requires a wide annulus rotor, whereas the C6(Z51) kits use a more conventional medium annulus rotor and pad height (~52mm).
Tobin
KORE3
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