I think it's a pretty good test. Although I think you took most things into consideration, weight, travel, ect.
Two things I think aren't terribly accurate though. If you look at the bag, the damage was a large area meaning the weight was pretty evenly distributed. Obviously our bodies aren't as conforming as sand, so we'd have pressure points, meaning more pounds per square inch doing a lot of damage.
The bag traveled 200 yards, which is a lot more then a person would travel. This means that the drag wasn't enough. Since the drag is what your trying to measure you'd want this to be much more accurate.