DPS-wise, Shred glyph versus Rip glyph, Shred glyph wins. Rip is a straight 4s increase, Shred is a 6s increase as long as you can Shred thrice during a single Rip, which you should pretty much always be able to do if specced fully Cat. Even if you so happen to be able to do it only twice, it's still the same bonus as the Rip glyph, making Shred glyph the clear winner overall.
Also, I have to agree with Galenmoon, Mangle is much easier to keep up than Rip. Longer Rips give you more time to prepare for the next Rip, while Mangle can just be reapplied at any time given you have the Energy.
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extended savage roar
There is no such thing as an "extended" SR, unless you simply mean to refresh it at 5CP's. The glyph increases the damage bonus by 3%, but not its duration.
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I would replace Glyph of Mangle with Glyph of Savage Roar. That's what I plan to do. Use Savage Roar, Shred, and Rip as majors
My thoughts exactly.
Berserk was shown to be superior on paper, but I don't trust something on a 3 minutes CD. At least not until I know every fight like the back of my hand.