The assumption in the paper was 100km/s which is definitely hyperbolic. If you slow it down to solar escape velocity at the Earth (the borderline of what you m

The assumption in the paper was 100km/s which is definitely hyperbolic. If you slow it down to solar escape velocity at the Earth (the borderline of what you might expect) you get 42km/s which is only a bit slower than in the paper. This would mostly have the effect of doubling your radiation exposure.