I agree that your ranking scheme is more reflective of skill. However, I wouldn't want to try and program the site to calculate the stat. Also, I almost never solve 4X4 puzzles and I never solve really high completion rate puzzles. But, I am always at the top of the list for lowest solve time. I'm averaging around 128 seconds per puzzle. You just have to do a lot of puzzles and have a mathematical mind and you can dramatically lower your times.