If I remember my high school physics: doubling the diameter of a hose will quadruple the possible flow. Even though you are not doubling the hose diameter, the 1/2 inch hose should push a significant flow though the 3 3/8 hoses. Having said that I'm going to put on my flame retartent suit...

Using 3 80mm rads is not a good idea, as you will get better efficency out of one large rad then 3 small ones. If you are hell bent on individual rads I would go with 3 120mm BPIs (roughly similiar costs) but less flow resistance.