Both systems work, if stands to reason that if you can accelerate to V1 @ 55° with 300.0 you will be able to do it even quicker if you weigh 250.0
You are basically using improved climb.
Around here people dont like fast V-speeds, so we use the speeds associated with the actual weight, the FMS produces the Vspeeds so this method eliminates the need for the crew to adjust the FMS for the limiting runway weight or the requirement to manually adjust the Vspeeds.
Mutt.