So...pardon my ignorance, but how are you defining a "tactical knife"? How is it different than a strategic knife? Is it different from a fighting knife?
I'm pretty much with Lt. Col. Fairbain in as much as any fighting knife ("tactical"?) Should have a blade at least six inches long. While knives will exsanguinate someone a lot faster than bullets, you still want to have enough penetration to hit vitals and open arteries. Most of the CCTV of knife fights I've watched, both in the street and in prison, the guys who sustain light wounds keep fighting, and the ones who sustain deep ones that hit arteries and bleed profusely can measure the rest of their fight in seconds. The alternative, if you only have a short knife, is the sewing machine attack used in prisons with short shanks stabbed as rapidly as possible to make as many holes as fast as possible. Once you've opened up an artery you mostly just have to keep your distance and wait for the guy to pass out, which happens very fast with their heart pumping in a fight. It is the very adrenaline that is fueling their fight that kills them by causing them to bleed out scary fast.
I can't find it, but there's video of a street fight somewhere in Asia where one guy gets just one good downward stab on the other guy's shoulder, hits the subclavian, and the guy goes woozy and passes out in less than ten seconds.
The Japanese have it down when it comes to sharp blades. Ichigo Ichie = one chance.
Edit-I am not the slightest bit squeamish, but about 15 years ago I cut my radial artery with a carpet knife, from the top wrist to the webbing at my thumb, and the amount of blood that poured and squirted out, in one split second, was astounding. I wasn't scared from the big wound, or the blood, but it was the amount of blood and how fast it came. Direct pressure instantly, and I was fine for the trip to the ER, but without immediate direct pressure it surely would have killed me in a minute or faster, and that was just a hand injury. It would have been a lethal wound in a fight if I couldn't stop and attend to it. Knifes are every bit as dangerous as guns when used as a weapon.