I would put the dual 10g card in the DSS and use MPIO with dual gigabit adapters in the servers.
A Dell 6224 with four 10G CX4 uplink ports costs $1,800.00 ($1,600.00 with just 2 CX4 ports) and you can use the 24 gigabit ports for 12 MPIO server links. I would dedicate this switch to doing ISCSI only.
Couple this with the SuperMicro AOC-STG-i2 dual 10g card (less the $500.00) and you have a cost effective ISCSI SAN infrastructure that should be able to support several virtualized servers and up to 2 DSS's if your doing failover.
SAN's are not cheap, but ultimately the way to go.