Good info.  I hope EMC ends up doing something like they've done on VNXe and implement Vault to flash.  It has been confusing the past several years with mixed messaging on whether to use the Vault for usable storage space or not.  On the old CX line it was always don't use the Vault.  It started to change around the CX3 timeframe with recommendations it was OK to use the Vault, but there were still a lot of doubters, and nobody would recommend it for anything requiring performance.  With the big emphasis on Pools, but you can't put your Vault drives in a pool, it almost seems like we're heading back to the old days of not using the Vault drives.