I'm doing the SL 5x5 routine and I'm not sure whether to keep doing 3 sets of BW chinups to failure the whole time, or switch to weighted chinups at some point. I started the 5x5 10 days ago and have gone from 8 reps (on the first set) to 12 @185lbs. At what point, if any, should i start adding weight and would it be 3x5 or 5x5 chins?