compression set of tin catalyzed silicone better than platinum? Platinum silicone is more dimensionaly stable, it shrinks less when it cures. 

However, i just need silicone which has good compression set (small change by compression), and perhaps, once they are cured, platinum and tin catalyzed silicone become the same material - silicone elastomer. Perhaps that tin silicone, having shrunk, is more resistant to compression set?

Does tin silicone have better compression set? Are the highest quality o rings made from tin silicone?
Tin catalyzed silicone lasts for a couple of years and platinum catalyzed lasts for 10 years, after which they lose their elasticity, becoming brittle and splitting. So while they may have equal properties for the first year, After a while the Platinum silicone will perform better. Using less catalyst for longer cure times also increases durability, and vacuum treating the silicone prior to casting and heat treatng it afterwards increases it's compression set performance.