A 400 inch SB is going to have very similar numbers to a 400 inch big block given the same head development. The SB will have a smaller bore size and a longer stroke so the torque curve might be a little bit different than a big block, but I doubt you would notice it.

If you are aiming for something in the 400 inch range then a SB will fit the bill. If you want something in the 500 inch range then a BB will be the easy solution.

SB engines get expensive to build once you start buying the good parts for them. An 800 hp W/R type of SB is going to be more expensive than a 800 hp big block with stock block and Indy heads.