In the data sheet for the 3750X, the network module (3KX-NM-10G) is described as being capable of taking in 2 SFP+ 10G interfaces, but it also supports 1 Gig SFP.  What are the attacehment rules for these interfaces?  Can all 4 interfaces be populated with 1 Gig SFP?  If I decide to migrate from 1 to 10, can I have three 1 Gig interfaces and one 1 Gig active at the same time?