I've been transitioning into the NB 900's for about 8 weeks now, and running around 30 mpw, at least 1/2 in the 900s and the other 1/2 in Asics 1080s. It seems that my knees & lower legs feel worse in the 1080s for the last few weeks. Is it safe to assume I can go 100% in the 900s or should I keep a day or two in them? I seem to do fine in the 900s.