What is the Difference between
Ultra S Crank Polished Pulley (Part#020611002) $170 Shipped
Ultra SS 3-Piece Polished Pulley Set (Part #040602002) $285 Shipped

Does the pulley set give you more HP than just the Crank Polished pulley?

 

The biggest HP gain is from the crank pulley.

However, getting the whole underdrive pulley set (Ultra SS) may or may not be a good thing.
Some people don't seem to like the handling characteristics of the new smaller power steering pulley.
If you have to have a set, then it's probably better to go for the stock-dimension set (Ultra SSc).
With this set you are simply getting a lighter set of stock-size pulleys; no underdrive.

I for one plan to get just the underdrive crank pulley (Ultra SS), not the whole set.

 

Most of the power gain is the lightened crank pulley. The other two are more for show.