What are your goals? You can make 700HP with a ported set of oval 781's with big valves on pump gas and a nice solid roller.
If your just looking for 700HP you dont need a huge head by any means... Im making 675HP on a pump gas hyd roller 496ci with AFR 305 CNC heads. If I were to drop an equivelant solid roller in I would be over 700HP per Tony Mamo of AFR. I drive my car everyday though and dont need or want a Solid.
Unless your running alot of compression stick with a 270-305cc head (depending on goals and use of engine).