Doesn't matter for calculating the non-Jewish White SAT is how I interpreted that. Since white_SAT = (2.4*jewish_SAT + 55.4*non_jewish_white_SAT) / (2.4 + 55.4), it means that even if your Jewish SAT estimate is off by ~100 points, it will only change the non-Jewish White SAT estimate by ~4 points.
Is there something non-scientific about estimates? Or do you think this is not a reasonable estimate, i.e. it may be significantly off? The charge of "non-scientific" is very vague - can you be more specific? What do you think is wrong, and by how much?