The Rim Light Effect

Looking to add a flash unit to my arsenal to use as a rim light. Would a 1600w unit that can go from full to 1/128 power work well as a rim light? Or would an 800w unit that can go from full to 1/32 power be better? Unfortunately I do not have the luxury of testing the units before I order.

Finally, what kind of modifier is best for a rim light? honeycomb grid, snoot, etc.?

Thanks for helping me out on this. It is greatly appreciated.

The power needed will depend on the power of the other lights in your setup. If you are blasting the front of your model with a whole lot of light, you might need a powerful unit for your rim light. And of course, distance will be another factor.

What do you have for lights now?

Using a Dynalite M500 pack into a 2020 head as the basis for this example:
250 w-s will produce enough light to need f/16 +0.3EV when positioned at 5' from subject. At 3.5' from the subject that light would be f/22 +0.3EV. If you dialed down the power on a 250 w-s light to 1/8 power, that would result in f/8 +0.3EV. In other words, it would be too bright if you wanted to shoot your portrait at f/4 with the main illumination, by 1-3EV (depending upon if the subject had black or brown or blond hair). So just imagine the problem of trying to use a unit which claims 1600 w-s output