Regarding O-235s in an RV-9, the Van's figures will be true air speed at 8000ft. I think DBo's figures are more likely UK based 'low level' figures - we don't tend to cuise at 8000ft in the UK.
...and vans use mph not knots... For a fixed power setting our IAS is pretty much constant with altitude. Pull out a calculator & an atmosphere table and you'll see that we're pretty much comparable with an O-235. we tend not to climb with full power (It tends to be a bit smoky - mechanical indirect injection's automotive equivalent is a black cab). But the full-power climbs we did for our initial permit matched Vans book numbers for 120 hp..
Dave