Viarmes

Hey, I have a question about keeping Savage Roar up. With Incarnation, SR is free for the first ~80 seconds of a fight, and after that, SR is refreshed twice as needed (42+42 sec). By the time that 2nd SR is near expiration, there will be 16~20 seconds left on the next Incarnation/Berserk cd. When I cast my 3rd SR, should I spend 1-2 cp just to keep it up long enough, or spend 5 cp for a guaranteed Predatory Swiftness?