I'm a little concerned as to why 2:1 Oversubscription is the best possible between the servers and the Fabric Extenders (e.g., 8 x 10G interfaces from the blades, with 4 x 10G Uplink Ports). If there is no QoS there (b/c there is no switching), then what happens if those uplinks get congested? It seems there is no way to prioritize the traffic until the Fabric Interconnect.
Over subscription between the Chassis & Interconnects is not 1:1...
The three options are 8:1, 4:1 & 2:1
Each blade has a single backplane link to each fabric. Two links per server x 8 servers = 16 lossless FCoE links total.
To manage congestion 802.1Qbb Priority Flow Control is used. Above & beyond that if you think you're pushing anything close to line rate you can implement 1000v & QoS.