I say SSD. Maybe those apps you mentioned could take advantage of more ram though the difference might just shave you a few seconds over minutes and even hours, anyway SSD will not just increase the performance of those programs (again maybe not as much as 8gb) however it will indeed increase the performance of the rest of the computer doing other stuff (that you will likely do) which 8gb will have none or little effect.
In the otherside $400++++ for ram makes little sence since in about (6months?
or less) they will cost what ram usually cost ~$50 for (two modules of max capacity) and upgrading to 6GB makes little sence also since for one part you lose dual channel (again not big deal for what you will be using it) and finally eventually you will want to buy 8GB so..
So overall go for SSD (they prices are likely to drop also, however I think RAM prices will drop more rapidly)