Martin says that 5 turns out on the limb bolts is the lowest setting that's safe to shoot. That should be a 15# drop from the 60# max. roughly, so 45#. That being said, I have a 60# Rytera that I have turned down to 38# for my girlfriend to shoot, and so far haven't had any problems. She's put a couple hundred shots through it, and it seems to be fine. I do realise that if anything goes wrong, I won't expect Martin to stand behind it though, having been shot out of spec.
2006 Rytera Bullet X 60#---2008 Moab 70#
2008/12 Firecat 60#--- 2010 Warthog 70#
2010/2012 Alien X 65# 2011 Onzas 60 & 70#
2009 Warthog 70#---2009 Firehawk 70#
2010 Strother SR-71 65# & 2012 Strother Rush 65#
I hunt, therefore I eat. lol