IMHO, it comes down to personal risk tolerance. I regularily do a "gut check" as to what I am comfortable doing with my abilities. Thal and a few others (myself included) had a discussion in another thread on how far down a wall we would go to catch up to a diver who was drifting deeper. The answers varied considerably but what I took away from it was that it is personal comfort level. I attempt to instill in my students not to exceed their comfort level but at the same time I can't define what their comfort level should be - I can only attempt to educate what the risks are and what skills and/or equipment should be utilized. Would I drop to 90' on 300 psi ... if I was the only diver at the site - probably, would I be successful - maybe/maybe not but nobody is going to tell me that I won't do it - that is my choice. I applaude the effort of all those involved in this rescue but I also have tremendous respect for the diver who had 300 psi in their tank and said, "no".