O-ring once bubbled...
Seriously, how much of a benefit are we talking about using argon instead of backgas (non-helium)?
At what temperature range do you think argon starts to become a necessity?
I wouldn't say it's necessary really. Depends alot on your suit, undies and personal comfort level, but for me, 55 and under is "nicer". I have been in 36 degree water for over an hour without it though. Not including mix diving, I get the biggest benefit on the longer doubles deco dives just due to in water time. With most rec style dives, it's a toss up whether to use it or not.
Phil