How would the SFP+ transceiver interface (Linear vs Limiting) affect my design?
I don't think it is that easily. 

The SFP+ requires an FPGA with a high speed transceiver. Not all FPGAs have those available and the ones who have (like Virtex-7) are usually not connected to the RJ45 connector of the development board. 

In order to be able to have such functionality, you either need an FPGA board that is already have a SFP+ like this board:

From High-Tech Global. 
Or purchase a board like this one: 

From Xilinx: 
http://www.xilinx.com/products/boards-and-kits/1-3y8uy5.html