I really hope this system is an improvement over stock in both sound and performance. Would love to have a factory system...but can't really run CF tips here in the NE with all the salt they use when it snows. I saw the 2.75" pipes and was surprised too...would think they'd run 3" the whole length, especially on a turbo'd truck.
Carbon fiber has no effect from road salt. It is non metallic so it would fair better than even the best stainless steel option. Also there is no reason to increase the pipe diameter since the exhaust is going to be restricted by the smallest part which is the downpipe. So until someone offers a turbo back exhaust, oversized exhaust wil only offer a sound change because of the increased resonance.