When lifting, pulling, pushing, or whatever, I focus entirely on form and heavy weight. I don't care if I turn in the slowest time of the day. I think I get better results (increased strength) by focusing on form and heavier weights than jerking myself and some weights around while trainers yell at me to not stop.
I'm not sure if I see the point of kipping. My goal is to increase my strength and ability to pull myself up not to increase my ability to do as many pull ups in a specific period of time.
When I wanted to do a pullup, I practiced doing pullups, not kipping. When I wanted to do kipping pullups, I practiced kipping, not pullups. Being able to do one does not mean you're able to do the other (I know lots of people who can only do one or the other--yes, this includes people who can do strict pullups but can't get the hang of kipping).