SPF+ module question

We've got some Dell FTLX8571D3BCL-FC transceivers in, on the server side Qlogic BCM57810 cards, and in our Dell S4048-ON switches, that connect to a Dell EQL 6110 San which I'm assuming are the same.  We're using this for all our iscsi traffic.  And I'm wondering if the "FC" is just a dell designation for these things or if this means something like Fiber Channel?  And I'm assuming they are OM3 Duplex Multimode capable?  We're having some weird performance issues and I'm trying to work out what might be the cause of it.