chasm54

As far as I can see from a quick glance at the Trek specs the Madone 3 WSD has similar geometry to the Madone 5 WSD. The frames are made of a different grade carbon fibre, but I'd think the differences are small and not something any ordinary rider would notice. So most of the cost difference is, as usual, in the components. Frankly, I'd be surprised if your wife could tell the difference between the ride quality of the two models.

At 6'3" I am hardly an expert on women-specific bikes. However, one of my riding buddies is a woman with a Trek 1.1 WSD. It's an entry-level bike with an aluminium frame, so less fancy and much cheaper than the Madone, but the WSD features are similar, and she really likes the riding position. Shorter reach makes her more comfortable and she especially comments on being able to manage the brake levers more easily - she has small hands.

Don't know the clearances on any of these bikes but you'd get 28mm tyres onto most things short of an out-and-out racer. I wouldn't get them onto my Giant TCR, for example, but there's plenty of room on my SCR (the predecessor to the Defy, with geometry more like a Roubaix). It's something you can easily check.

It is certainly worth having a look at cross bikes, but if you already have Tricross comps you know a fair bit about the differences between these and road bikes and what extra the latter has to offer. Only you can judge what that means to you. And if the priority is comfort and a relaxed riding positions rather than speed and sportiness, a light touring bike might be worth a look. Something like the Raleigh Clubman? Steel, a lot heavier than a CF Madone, but versatile and still fun to ride.

But in the final analysis, what matters is how one feels on the bike. If the Trek WSD geometry feels perfect to your wife, then you are going to search a long time before you find anything that suits her as well. And having a bike that just feels "right" is well worth a small premium on the price, in my opinion.