Slight necro but it's relevant.
My character has over 800hp (high level warrior with decent strength, endurance and Body Development advanced skill) and I managed to survive the 3rd Physical Enhancement. 3rd one just says "critical failure" and doesn't give a trait. I healed up and tried again, and the 4th Physical Enhancement did the same damage as the 3rd, and also didn't award any traits. So yeah, I'm pretty sure that you can get 2 trait points max from these things, as the 3rd try is designed to kill anyone but the tankiest of characters (which is probably the reason damage didn't increase for the 4th try).