[mannykannot]

One detail: V1 is the last-chance speed for being able to abort the takeoff within the remaining runway length, but it is predicated on the weight, among other things, being correct. If the airplane is heavier than the figure used in calculating it, you will not be able to stop in time from V1 (you will reach it later and further down the runway, yet need more distance to stop.)

Having said that, a speed-at-distance rule like the one you give here, especially if it was evaluated at a distance before you expect to reach V1, would be perfectly good. There is a rule-of-thumb for small-plane pilots saying you should have reached 80% of the rotation speed before you are halfway down the runway (though that speed is also weight-dependent - as demonstrated in these incidents.) There is a tacit assumption here that your deceleration after choosing to abort will exceed your acceleration up to that point.