Hi Bill,
I know too little about the S17 to be able to offer specific advice.
But generally my experiences with selfbailers on Swallowboats are as follows: Smaller Elvstrom (wedge-type) selfbailers work relatively more efficient than the larger ones. SuperSuck (Venturi principle) start to suck at lower speeds and suck longer, only downside is they lack a non-return flap. So during each tack or slack you see some water flowing back in.
All deciding is speed through the water, with the Elvstroms expect no miracles under 4.5 knots;
and do not mount the bailers too deep in the hull, better further up where the water actually gathers when the boat sails well heeled in a blow, that is when you will need the bailers.
Hope this helps.