Eddy Classic IAS shock vs. the Eddy Performer IAS shock

What are the differences between the Eddy Classic IAS shock vs. the Eddy Performer IAS shock for the same vehicle? http://www.summitracing.com/search/...and/Edelbrock/?Ns=Rank|Asc&rsview=ProductName

I posted on the Edelbrock site, but didnt get any response.

Thanx in advance,

Bad Shrimp