good question as I am planning to do the same with my two 300gb drives. Reading other literature I see that multimedia is better starting at 64KB stripe where smaller files like docs are best at set the stripe much smaller. However in reading many other comments I see guys that have setup up their stripes at 128kb. Looking at the HD benchmark results I see that seeking and transfer are directly related to stripe size (at lease that is what I belive for now). But reasoning would make you say that you can reach a point where the size of the sripe is to big and would then slow down fle transfer.
All I can really say for the moment, te jury is out on what size stripe is best for you?
I am curious to see what you have chosen.