2 ways to take this ... both ways Combat Speed = Finesse

First way, simply have movement (on strategic and on tactical) and finesse.

This would be, like someone else has said, Movement = action points, and an Attack costs AP/Finesse, while moving 1 tile costs 1 AP.

Alternatively ... you could have Movement (tiles per turn on strategic map), Speed (tiles per turn on Tactical battle), and Finesse (attacks per turn on tactical battle).

In this case Speed = AP, and an Attack would cost AP/ Finesse

Finesse is identical to the current (combat speed).