I've been really happy with my Enve SES 8.9s. While I probably could have gained a couple seconds with a disc, the Enve's have been bomb-proof in both training and racing.

In ideal conditions (without crazy cross winds etc.) a deep dish in the front and a disc in the rear is the fastest set up possible!!.... either way, the difference between two deep wheels and a deep front/disc rear is marginal at best. The wind tunnel data is out there somewhere