I am not very experienced with studio lights but I've researched them a bit in the last few months and I would like to add a couple comments.
First is that from my understanding, the Ws rating is not really a normalised and directly comparable measure. It should be comparable within a given brand, but might not be between brands. For example, the light output from similarly rated lights might differ because of the tube and electrics\electronics efficiency, reflector geometry and reflector efficiency.
Second, because your actual flash has 5 stops does not mean that a lower powered flash will also have five stops. You might pretty well have a 4 stops 250Ws light that has the same minimum output as your larger strobe. Apparently, the actual precision and range of adjustment appears to be one of the most evident compromise of cheaper strobes.
I didn't really think about that - different brands having different ratings, but it makes sense. Fortunately, I have two Bowens 500R's and I'm thinking about getting the 250R's to go along with them. I would imagine that they would have similar performance, only the 250's would be a stop dimmer at both ends compared to the 500's - the 500s are 15-500, and the 250s are 7-250.