on a small port ARZ motor I'd set your sights on 230bhp and be very happy if you reach it. The honest truth is that there are almost no cars out there making a genuine 250bhp from a ko3S, and those that are are right on the limit and don't maintain that level for many miles before things start to give up.
Figures are pretty meaningless anyway, as it's all about how it drives.
I assume you'll be getting Niki to map it?