Hop comparison test batches

I'm doing some 2.5 gallon extract pale ale batches for the sole purpose of comparing different hops. I need some feedback about how to do a good comparison. I'll be using the same extract and yeast for all the batches and I'll be buying the hops in 1 oz pellet packages.

For a good comparison, should I try the keep the IBU for each batch about the same?

To do that, should I vary the amount of hops, or vary the boil time? I'm leaning toward boil time because I don't have a scale and could probably only accurately split the 1oz packages into quarter ounces.

I think keeping the IBU's the would be good. It should give you a good comparison of the flavor each hop variety adds to the beer. However, IMO I think you might want to get a scale and adjust the amount you add to the boil. I think it would be difficult to control IBU purely by boil time, particularly if you are trying to compare something like a13% AA hop to a 3% AA hop. But it is a cool experiment.

To be more specific, I guess I was worried that for a high AA hop I would have to use a fraction of an ounce to hit the desired IBU (35-40). So, for example, I would have to use 0.35 ounces (hard to measure) of hops for a 60 min boil or use a half ounce (easy to measure) and a shorter boil time. For lower AA hops, I plan on buying however many ounces I need for a 60 min. boil to get the desired IBU.

Look up the thread discussions on SMaSH beers. (Single malt and single hop) beers. You'll find a lot of good discussions.