I would definitely use different amounts depending on the alpha acids. Go download a copy of SUDS and make a basic Pale Ale recipe. Then brew your batches so that they all have the same IBUs, but use different hops. Then you can *really* tell the flavor difference.
One thing is, some hops are just intended for aroma/flavor and others for bittering. Saaz is really never used for bittering, and it would be kind of expensive to waste them on bittering because you'd need so much (because of the low alpha).
I'd consider choosing a standard hop for the bittering...say 1/2-3/4 oz of Columbus in a 5 gallon batch. Use the same bittering hops in all the batches and then vary the finishing hops. That way the overall biterness of the beers is identical, as is their body, alcohol, etc. The only difference is the flavoring/aroma hops. Bittering hops don't contribute much flavor anyway, so it's a shame to use something as wonderful as Saaz as a bittering hop.
BTW, we do this all the time in order to get to know a hop and really isolate its particular flavor. That's how I first fell in love with Centennial, and we just brewed one a few weeks ago with flaked barley and all Chinook called Flaky Salmon.
Have fun! Sounds like a great project.
