I can not resist this opportunity to get in a shameless plug for my personal favorite.
My Panther fighter fulfills many of the relevant requirements. It is fast, concealable, and can stab or cut with amazing efficacy.
Witness the goat mauling we did at EWC 2000.
Two deceased goats were hung in the dojo, and myself and the attendees were allowed to make cuts or stabs on the carcasses.
The 10" Panther was easily capable of severing both arm and leg bones while they still had the flesh on. It was disconcerting to some to witness 7-10 pound chunks of meat hitting the floor after the cuts were made.
One cut even severed the spine in the lower pelvic region, dropping the entire lower end. Another cut went through six ribs on one side, and four on the other, after passing through the sternum at a depth of seven inches.
Photo of the Panther at link below:
http://www.mdenterprise.com/panther.htm