Both rivers should have Springers in by that time in April. They won't be in the large numbers that it would be in May, but they will be there. It depends on your experience running rivers and what kind of boat you have. The Sandy is a bit easier for Drift Boats from Oxbow down. Below Dabney would be best, but you will share the river with Jet Boats. The Clack is pretty easy to run from Carver down, and again you will share w/ Jet Boats.