I use both C4D and Carrara. An upgrade to C7 is pretty insignificant in dollars compared to C4D. Additionally, some of the things that Carrara does out of the box like Global Illumination is an additional add-on to C4d (like particles, physics, etc.) unless you're planning on getting the full Studio. C4D Studio is an excellent package but it's also $4000.

For modeling clothes for the Poser/Carrara community Carrara is probably your best bet in money and learning curve. Carrara, especially compared to it's price, is a very full features program.