Let me rephrase this question.
If you had 20k to build a video editing network what would you buy? Hypothetically, you already have a 10gbe switch and the Mac Pro editing machines.
Basically, would you go with NAS or SAN. What RAID (NAS or SAN) box would you buy and would you use tape or not? There are three editors and maybe five in the future all editing in Pro Res.
QNAP, Drobo, Small Tree, EMC, …?