Best 10GBe Card for iSCSI ?

All,

your oppinion on iSCSI and 10GBe Cards please:

a) Chelsio Communications: N320E-CXA T320 based with software iscsi (CO on HCL!)
b) Chelsio Communications: S320E-CXA S320 based with hardware iscsi (no HCL entry?)

c) NetXen (QLogic): NXB-10GCX4 with hardware iscsi (CO on HCL!)

Or should i stay on current Intel X510 Cards (Intel Corporation 82598EB 10-Gigabit AT CX4 Network Connection (rev 01)) ??

Usage is 80% iSCSI for VMWare ESXi 4.1 and Windows 2008 R2 with Exchange 2010.
Today we us an older DELL 2970 / two 10GBe Ports in Bonding Mode (balance-rr).

The DELL 2970 will be replaced with DELL R715 beginning 2012 ...

Any experiences with card a), b) or c) ??

Thanks

We use the Intel X520's with direct attached copper cables.

http://www.intel.com/content/www/us/...rnet-x520.html