I would go with FIC, a lot of people run reflowed injectors through FIC. I would also go with the larger of the two. You can always dial it back, if you run out of fuel with a 37 you will need to go with a bigger injector for any future upgrades. Then of course the 42's will have a limit as well.
Then you have to think about the pump and other supporting fuel mods as well. I am un educated with the LS motors. So im not sure what the factory fuel system is capable of.