Seek and ye shall find
The issue of range was really “how far can we see”, as the light’s range did vary a bit with fog/mist, rain, dust, etc. Even my M551A1 Sheridans had lights, and I once (ONCE) hit a target at 1400 meters in an otherwise pitch dark night.
Here’s the secret: searchlights are literally line-of-sight. The guns all (to one degree or another) require superelevation. Our battle drill was to light up the targets with backlit mortar illumination rounds (first: 4.2” is great for this), and then blind them (briefly) with the searchlight. A second tank was the shooter, and did not use the light in typical gunnery situations. Coax against troops and lightly armored targets could be done (coax max effective range is ~900m) with your own light, but we emphasized using the light for VERY short periods of time.