As a consumer the BTw estimate isnt relevant sadly, its informational purposes at best. Also that handback threshold is a complete joke, its about 20% of the upper estimate so BTw thinking its ok to provide a massive 80% acceptable performance swing of line capacity.
Lucky for you plusnet have at least decided to put bigger emphasis on the clean vs the impacted estimate and are nowhere near the handback threshold, but that is a very wide estimate covering 33% of the max potential speed, something I feel has got out of control on FTTC and needs cracking down on.
So you at 18mbit down, estimate of 24mbit down. Those are the two important figures, providing the line is stable the speed should increase on switch to g.inp but by how much I dont know, its a wait and see. There will also be possible further improvement after that if the target SNRM gets reduced. I feel after DLM has found where it wants to be you will either be above 24mbit, in which case the line is in its estimated performance window, or not much below it, and plusnet would probably need a big push to consider it worthy of action. Fingers crossed the line is stable enough for a DLM profile to get you above 24mbit.