Good point, Peter.

Keep in mind, guide numbers and watt-seconds are two different things. I have a (yes, just one so far!) 750 w/s monolight with a guide number of 350. It has enough power for just about anything, although their smaller 375 w/s has a guide number of just over 200 and would be pretty versatile as well depending on what you're doing with it.

Put it this way, in my little bit of experience it's pretty easy to get F11 at ISO100 shooting thru an umbrella at 1/2 to 1/4 power. Obviously there are a lot of factors that affect this, but just a quick example.