Not really, especially if you are new to type of software. The shaders are quite different but in may aspects RDS 5.5 has more features in it then Carrara. Your added benefit would be that you would be able to upgrade to Carrara at a special price when it is re-released so it is a win-win situation (if you can get RDS for a good price & it is legal). Most of the modelers & actions are very similar between the two so you would still be learning "Carrara" while learning RDS. I'd say go for it.