Depends on the flows and conditions for me. In lower flows and clear water, I'll throw smaller lures. Higher flows and more turbidity, I'll throw bigger lures. On the rivers I fish, prespawn water temps range anywhere in the 50's. With that said, throw a variety of sizes and profiles until you find what they want. As you stated, low-mid 40's, I personally would work slower, but I we're fishing different locations. Every river system is unique with its bass behavior and forage size and type.