Just curious, but how much ram did you need?

I'm try to get a rig of 5 cards up and running. I initially bought 4 GB and have more on the way. Wondering if 8/16/32 is required for 5 cards. Right now I have 2 up and running with low intensity just to have something hashing. Hoping 8GB for 5 cards will be enough, but anyone's input would be appreciated.

Edit: Running ASUS R9 290 cards if it matters.
M5A99FX PRO R2.0 AM3+
GSkill Ripjaw 4GB ram
sempron 145