well from your question I can read, that you would like to buy a new Macbook Pro! Take the 15"!!!
I am an architecture student, which uses Cinema4d, I installed it, but I never used it on my new 13" machine, because I didnt need it in the past weeks.
But generally i feel very unhappy with the 13". I should have bought the 15" and preferably the highend one.
I upgraded mine with an SSD and 8GB RAM, but using CAD everything is not as smooth as I wished before...
I think, I will use my macbook pro 13 until Ivy Bridge, then I will substitute it with a high end 15"..... Or buy a PC Workstation... Dunno...