x2

you will not top out a cx tranny in any sense so they are out of the question in the performance standpoint unless you had enough power to make use of the cx ratios. You've stated you're using a b7 so an ex tranny would make the bank for "street power" or "street speed."

I've used dx, cx and ex (oem internals) on my boosted setup. Before i boosted i researched the trannys available and the gears available as well as the final drives for quite a while. There are many setups you can run combining gears from different honda trannys but as far as stock box trannys go here are my thoughts.

The cx never did any good (except gas mileage).
The dx was nice for autox as the final drive is 4.058 and gears were spread a little more so there were less shifts involved.
The ex tranny is has closer gears and a 4.25 final so the the rpm drop from gear to gear is lower and the gears will rev out quicker thus having the greatest acceleration. (if there is grip to be had)
All d series first gears are the same but will feel different due to the different final drives. I could go on for a while with d-tranny talk but just pm me if you have any questions.