The last two posts say it all. High end mixtes are hen's teeth. I think one reason is that most mixtes tend to be urban and utility bikes, and even the nice ones are more for touring as opposed to racing or fast club rides. I've never seen a woman ride on a mixte on a fast club ride, and the ones I know who race--nope, they're all on carbon.

If your problem is keeping up with your husband on his Columbus-tubing road bikes, then get an all-out road bike for yourself that fits you. If you still can't keep up, tell him he needs to slow down. Life is to short to drop your wife when she's willing to ride with you. When I ride with my wife, I kick back and go at her pace--I'm in no hurry--it's all about fun--and we still cover some miles going slow and steady.

And really, the only thing special or different about a mixte or step through is how you get on and off the bike--nothing about them makes them more suitable for women riders, unless you ride wearing a skirt.