[fpernett]

Hi Pat
Well, I don't think competition stress is only factor, there are other issues like your previous training. Stress can be helpful but also can ruin your dive.

If you're training to have a strong DR, you don't need to care much about CO2, let me explain:
A strong DR isolate the muscle cells from peripheral circulation, it prevents that O2 coming from circulation enters the cell, but also keep the CO2 produced in the cell. Many experimental trials have found that the EtCO2 is lower than expected specially in CW dives, and is possible also to have some CO2 transfer reversal in the lungs. (Craig, A.B., Jr. and W.L. Medd, Oxygen consumption and carbon dioxide production during breath-hold diving. J Appl Physiol, 1968. 24(2): p. 190-202.)(Ferretti, G., et al., Alveolar gas composition and exchange during deep breath-hold diving and dry breath holds in elite divers. J Appl Physiol, 1991. 70(2): p. 794-802.)(Boutilier, R.G., J.Z. Reed, and M.A. Fedak, Unsteady-state gas exchange and storage in diving marine mammals: the harbor porpoise and gray seal. Am J Physiol Regul Integr Comp Physiol, 2001. 281(2): p. R490-494.)
So the starting CO2 will affect mainly your respiratory center, and flow regulation in heart, lungs and brain, not diving muscles. With strong hyperventilation, the urge to breath will come late, but the alkalosis impairs the brain blood flow, and the hemoglobin saturation curve shifts to the left side, so less oxygen available to brain and BO. On the other hand, strong hypoventilation will make you have earlier contractions, in CW more narcosis but better blood flow.
I think you don't need to change the way you breathe. I think the best way to go is with Normal CO2 (also normal pH).
This is just my opinion.