Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I would suggest to wait until you actually begin work on your movie, this would give you time to wait for montevina, usb 3.0, ddr3, mobile quad core, maybe even blu-ray (probably only in a mac pro, but it might help you out since your into film)

I would probably say that the guy who said to take the lowest version possible is probably wrong. You could get the processor power, and still just get re-seller RAM, which is very cheap (unless theres an upgrade to ddr3, where I wouldnt know what the prices would be like)
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.