The USAF and the FAA tell us that the human body can survive sustained 9G declaration. To the point that it has become (I am led to believe) the requirement for structural integrity of seats and cockpit in N registered aircraft. I can't find the study right now but will research it if anyone is actually interested, that looked at deaths related to deceleration in aircraft accidents. 100% of cases where the deceleration was 9G or less were survivable, yes higher transients up to the low 40's were survivable, albeit with some nasty injuries, but the tolerance was in the tenths of a second. I am talking sustained here. So, for my money the key is hitting the ground and stopping while sustaining 9G or less. At 50MPH you need 9.4 feet (all I could find was in US language) at 100mph you need 37.6 feet. So, the key is to arrive in control and as slowly as possible. Some of the 9.4 feet can be crumple zone of the aircraft, wings, and anything you need to hit to slow you down. But when you think about it 9.4 feet is not all that far if it means survival....