At the risk of restating the obvious, the faster you go, the more drag "outweighs" weight as the critical factor. If you're focussed on hard and fast numbers, weight is easier to quantify than drag, but that doesn't make it the dominant factor. In raw speed terms weight affects speed in the form of the induced drag generated by the wing carrying it. This is governed by the L/D of that wing at that weight and AOA. The SBD, being a dive bomber with a load carrying and dive recovery requirement could be expected to have a wing designed for optimum L/D at high loadings. This lessens the significance of weight vis a vis top speed, but can be valuable in terms of reduced energy bleed in high G ACM scenarios. We know historically the SBD was good at this. Where weight makes a big difference is in acceleration, climb performance and general agility, to include turning ability.how much of the speed difference between and SBD and say, a Buffalo or a Wildcat is due to drag as opposed to weight
The real speed enhancers in this case are serious drag reduction and anything that can be done to increase effective thrust.
I think a sleek, streamlined, lightweight "SFD", while no speed demon, could have made an effective early war secondary fighter in the F8U/F4B model and could have been a useful counter to the agility of various IJN aircraft.
Cheers,
Wes