I've shot both bows, and ended up getting a FC400. I had an older FC before, so it was just a natural for me to get another. The Onza is a great shooting bow. It actually felt a little "deader" in my hands, and was just a touch quieter. I don't think you can go wrong with either bow. Just have to shoot both side by side, and make your decision on which you like best.
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