I use P7 content all the time with Carrara. I started out with poser and was always so unhappy with the render quality. The default settings in Carrara are better than the finest tweaking in poser.
Using poser content in carrara definitely goes more smoothly in the latest version (C7). None of us can really say about the new version of Carrara express, which is much cheaper, but is not released yet.
Remember: DAZ has a trial download and 30 day return policy, so you can give it a try.