4 seat Final Cut Pro HD Xsan set up

I am trying to get some clarity on the hardware requirements for a all HD 4 seat Final Cut Pro HD/ Xsan Xserve RAID setup. The setup needs to be able to handle about 16 HD streams (4 per edit system) simultaneously at all times. This is a sort of mission critical broadcast application. I am assuming a 160MB/sec sustained access rate per HD stream to base my hardware config on. Each Xserve RAID has 2 controllers at about 80MB/each, right? Here comes my flawed math: I figure 160MB x 4 (on FCP editor w 4 realtime HD streams ) and multiply that figure times 4 to get to my overall IO requirement of about 2560 MB for the whole setup. Now I divide that by 160 MB (Xserve RAID IO capacity w 2 controllers) and get to 16 Xserve RAIDS required. Is this crazy or realistic? Thanks much for reading and for providing this forum.