You can put in a 1Gb RJ45 transceiver into many SFP+ ports (not all - check the Quickspecs), but that will only give you 1Gb. I have not see a 10Gb SFP+ 10GT transceiver. I have heard rumours that they are exist, but I think there are issues with the MSA spec and PHY support (mostly to do with power) that make them non-standard at present.