This is a really tough question to answer because it's kind of "what you can tolerate". Some people will spin an unbalanced staff and not care. Some people will spin it and say "this is horrible!" LoL. It's kind of like, how much shake can you deal with in an unbalanced tire in your car? Are you the kind of person that doesn't care if your steering wheel shakes a little or are you the person that takes the car in to get the tires balanced every 3000 miles?
If you think about it that way, it might help you decide what's best for you... I'd vote for getting two RGB CE Prophecies, but that's just me
Even if you have to save up a little extra money to get dual RGB, its sooooooooooo worth it. My Prophecy RGB CE is my absolute favorite saber. I'm always cycling through the colors on it. Having two of them would be pretty freaking awesome LoL
OMG, now that you have me thinking about it, now I want to buy another one to make a staff out of it!