Standard catalysts are mostly ceramic, sports catalysts tend to be made from stainless steel and therefore can stand more abuse without failing.
Inside a catalyst is a honey comb type structure which is measured in cells per inch. The higher the number the smaller the holes and the more restrictive the catalyst. Standard they tend to be around 600 to 400 cell, whereas Sports catalysts are anything from 100 to 200 cell.
Noise… Small increase in noise and a few nice pops and bangs.
Performance... A small increase in performance any where between 7%-10%
Weight Saving… A Sports catalyst is considerably lighter than a standard Cat.
Most performance silencers are a straight through design in which the exhaust gases pass through a single perforated pipe into a outside chamber packed with sound absorbing (or insulating) material. As the exhaust gases expand from the perforated inner pipe into the outer chamber, they come in contact with the insulator and escape to the atmosphere under constant pressure. Because of this, the expanding chamber tends to equalize or spread the pressure peaks throughout the exhaust from each individual cylinder of the engine. This type of silencer is lot more free flowing and designed for the purpose of reducing back pressure so giving performance and consequently makes slightly more noise.