Chris - if I were you I'd definitely go for the macbook pro.Â
I currently go from a 12 Core Mac Pro to an 11" Air - and working wise I actually don't notice a speed difference. Like... at all. I'm almost sad to say it. But happy at the same time. Of course I've always tried for optimized workflow with precomp etc. - importing images that are pre sized and what not. But that's just good workflow on any machine.Â
Renderwise in c4d you definitely notice it - but for all other things - might as well have the portability. I send stuff in c4d to a farm on my girlfriend's older iMac and her new MBP and the MBP far out does the iMac. So you'll probably be pretty happy with it.Â