I've had good experience with the Unorthodox Racing pulleys.
Here's what I have to say about underdrive:
I have underdrive so to compensate for my added stereo equipment I got an Optima Redcap battery and a 2 Fraud Capacitor for the stereo stuff. After that, I have had minimum problems with lack of power.
However I will add, I used to have HIDs in the car. With the HIDs everything was fine, but now that the stock lights have been swapped back in, I do get slight dimming. If you need the power, I'd recommend stock diameter.
The underdrive actually made a noticable difference though. I don't have a HUGE number of performance modifications done but the legacy is definately running a good amount faster than stock.