The 1RM calculator is pretty reliable, given you do a 3RM heavier. Any lighter than a 3RM, and energy systems, lactic acid, blood occlussion, etc. come into play and make the calculator worthless.
Anyway, I heard a story from one guy that when he used bands, his squat gained that much in just a week. Then again, he was squatting in the mid 300s before he used them.