While I can't speak for t5xt5 breeds. The T7's and T8's I breed turn out fine. No heavy setbacks ... I just jinxed myself to post this but w.e. I even got a T8 male that (through leveling) turned out with 17 skills and only 1 change coupon. For me that's quite lucky. Usual results from breeding are 2/3 T7's and/or T8's for 1 t6 female. I'm fine with that, I just go and breed my T6 females with my T7 males.