Typically unless you do a big ease or have a very heavy duty vang made up snug, easing the main sheet initially powers up the main and can give you more heel and require more helm to hold your course slowing you down.
In short duration and small speed increase gusts, feathering up increases VMG without losing speed Depending on your
rig and how your backstay is set up, putting on a bit more backstay can help with heeling and VMG as well. Dropping the traveler works on gusts that are of longer duration and larger velocity increases.
The reason that you turn down wind when below a beam reach is because your boat speed is subtracted from the windspeed the further downwind you head, and you boat speed increases as you head down toward a broad reach.
Jeff