Hi ToMang07,
All of the FiTech efi systems use the same 900 cfm throttle body. I believe their HP ratings are based on the fuel requirements for a given HP. They increase the number of fuel injectors to increase the HP capacity/rating. I guess it's possible you could have enough fuel, but run out of cfm capacity at the higher HP levels (at higher rpms), but I think you'd be fine. I just don't see many big block owners running 1000 cfm carburetors, unless they have all out race motors that have much more than 500 HP.
Travis