How Many Milligrams of Caffeine is Too Much for a Pre Workout

I am looking at different pre workouts and the caffeine dosages are all over the place. Some have 150mg while others have 450mg. I am wondering how many milligrams of caffeine is actually too much for a single serving. I do not want to put too much strain on my system.

I am in Canada and I generally have a good tolerance but 400mg seems like a lot to take all at once. Is there a sweet spot for performance where you get the benefits without the negative side effects? I am also thinking about the total caffeine I have in a day including my morning coffee.

What is your personal limit for caffeine in a pre workout? I am trying to find a balanced product that gives me a good boost but still feels safe. I would love to hear how you guys decide on the right dosage for your needs and your body weight.