Ralph, yes the fatty content is different. I found 131 to be good for strips. And 6-7 hours seems good to me.
If you are cooking at 129, I would try to push it out to 4 hours. Some will say for food safety bump it up to 131. But I've done ribeyes at 129 for 4 hours many times.
Experiment and have fun. I think you'll be eating good either way.