I have the four pulley set on my 99 SE-Limited. It was the best engine mod I have done. Power increase very good.
I had it done at Dealership it is a 4 hour job with the right tools.
I also have: CAI, Cat back & Cams. Pulleys was the best bang for buck upgrade.
Save your money and go with the 2 set. There is not a significant difference except for looks if you go with the 4 set. I'm getting the 2 set from my girlfriend for christmas. shh don't tell her I know what I'm getting.