if you're talking about the 4-2-1 headers, these are definatly on my list for stage II. Accordign to what research i've done, the step design significantly increases low-midrange torque much more than basic longtubes. The tradeoff is that your high end power is a little bit of a loss, but then again, unless you're planning to hang out in the 5-7K RPM bands all the time the Bassini's are going to be best.
even when drag racing the time spent in the 5-7K Rpm band is relativly small compared to the time spend between 3-5K.