Its always difficult to fixed on one caliber for all. Ofcouse powerful calibers can kill it all but are they adequate for a bunny hunt?.If I should come up with a careful choice for european game the 6,5x55 would be slide in the middle as a compromise. As an all-purpose gun a side-by-side(büchsflinte) with a 20bore in the right barrel and a 6,5x65R in the left barrel.