There are lots of things to consider - in general the cylinders the more drag/parasitic losses/friction in the engine, so less power would be seen at the fly given the same volume of air and fuel being burnt equally well. In terms of revability, assuming equivalent head designs, equal compression ratios etc, so as to give equal VE's across the rev range, the difference would come from how well balanced the different configurations are, weighed up against the mass of the rotating assembly (specifically its inertia, which is proportional to mass). A 180degree V8 is the best balanced rotating assembly, IIRC, but also the heaviest so although it would feel smoother at higher revs than the inline 4, it would take longer to get there.

Chris