The TOW wire is 3,750 meters long. You'd always see people out in the middle of the night in the impact area trying to recover it to sell to recyclers. My experience is mainly with the Cobra mounted ones. I trained on a ground mount only once, way before I went to flight school, but the system was the same. Just the launch platform is different. On the Cobra you didn't recover anything obviously since you're in mid-air. There's a wire-cut feature that severs the wire, either on command or when the wire pays out, so you don't drag some 2+miles of wire around with you. We could get far longer ranges than the ground mounted one by flying forward and chasing the missle so the wire wouldn't payout as fast. The missle looses effectiveness at that range because of angles, etc that the missle has to fly to maintain altitude. It's not pointing "dead-on" at 5KM, so there's a lower chance of penetration. Still, it can be used advantageously in certain situations to extend your reach. The bigger problem is identifying the target at that range with 13x optics in the TSU.
The answer to your question is 3,750 meters if you just took the wire out and streatched it out straight.
Ross