So let me see if I have this right. First, an unknown is how threat modifiers really work. What I mean by that is we don't know what makes a +1 to the threat modifier. My assumption would be X amount of damage is equal to Y amount of threat modifier. Without knowing that, its tough to say exactly how long you will hold the monster after a successful intimidate.
In the OP video, my + was 66 on the die roll. That's after size modifications are taken into effect. So my small buffer would be (with a shield on) 2 * 66 = 132. Any extra melee threat % I'm wearing at the time, will increase that number by that percentage. So, if I have 50% extra threat on at the time of the intim, I'd get an extra 66 on top of that 132 for a total of 198 for my buffer.
Will 198 be enough of a buffer, without me doing any damage, to keep aggression over say a barbarian doing average 300-400 damage a swing for 15 seconds? Only time will tell unless we know exactly how much DPS = 1 Threat modification.