I curently have both. Your best bet is to do the same, modelling in rhino is superior in just about every way, and if you can learn to use it, then i say get it. (Also if you have autocad experience then definitely go for it). As for carrara, its far superior renderer can make anything you've made in rhino look like a dream. Exporting in 3d studio format is the best method i've found. Good luck!