I think 20 bits is too small. I've been looking for a source without success; the closest I've found[0] is 32-75 bytes per key which is something like 11 milli

I think 20 bits is too small. I've been looking for a source without success; the closest I've found[0] is 32-75 bytes per key which is something like 11 million keys per GB of RAM. [0] http://www.quora.com/Matt-Heitzenroder http://www.quora.com/Matt-Heitzenroder