10G
Strobes are neither needed or wanted. In actual use they adversely affect the end user when they should simply be trying to focus on a threat's hands or search an area. They can make it difficult to catch critical details that are phenomenally important. Those details can make the difference between shooting someone or not, getting shot, or not, and making mistakes that may cost you beyond what is immediately happening, later in a court. The only people I generally see recommend strobes are those with little to no experience. Generally "Good Idea Fairy" fairy types. I have had my gun out literally thousands of times doing building, area searches and holding people at gunpoint, etc and I very definitely do not want a strobe. Just a light with an on off feature. No gimmicks.
As far as power, for a pistol mounted light, 600 to 1K is fine. You use it to see what may be in a person's hands, to ID threats, etc. You need to have a separate handheld light though. People with pistol mounted lights and little training tend to get accustomed to searching and ID'ing bumps in the night with their pistol.
In practical exercises training people, when you put them under just a little bit of stress, 95+% of people without extensive training will automatically point their pistol that has a light attached to it, at whatever they perceive to be a "possible" threat, long before they have verified it actually to be one. In role playing they point guns at little 14 year old kids who are sneaking around their yard and in and out of the house, doing dumb things kids do.
The problem is that not every bump in the night, or even a fraction of them are lethal threats and you are pointing a deadly weapon at something that you should not be. Not trying to start a debate, just reminding you to also have a separate powerful handheld light for actual bump in the night investigatory tasks.