Berkley Vanish is stiffer/less stretchy than Seaguar CarbonPro/Invizx. On a straight even pull Vanish is stronger, but its prone to breaks (while actually fishing) in the lighter diameters. But 6-8lb Vanish tippets are great and have landed hundreds of steelhead for me.

So right now my main setup is a level Vanish leader in the 8-12lb range with a Seaguar Invizx 4-6lb tippet when necessary.