15% increased Damage would be spent anywhere for a cat. IN fact shreds or mangles will yield more dmg than you'd get over time on a rip with say a full duration of TF.
If you have your 4 set t13, your rip will constantly be refreshed anyway sub 60% on target.
The highest parse Ive seen in cat is with a high up time on SR stat prioritizing haste > mastery..... and a decent uptime on rips Pre-60%....after that its all about Mangle on target - Rake - Shred > once at 5 CP,,,Ferocious Bunghole (Refreshes rip)...all the while keeping SR up as well ( I usually do 3-4 CP Sr's)