Had a couple of configuration tweak ideas:

First

Have a Max stat limitation for each chicken...e.g. you can specify that diamond chickens cap out at say 2/2/2, or ender pearl chickens at 4/4/10.

Second

Have some sort of cross breeding limiter (similar mechanic to agricraft cross breeding) for each stat (Growth/Gain/Strength), make this a decimal value between 0-1.

This limiter gets applied to the scores of the new egg produced by cross breeding:

Configuration value (missing) == keep the original calculation
Configuration value= 0 ==reset the given stat back to 1
Configuration value= 1 ==keep the originally calculated stat
Configuration value between 0 & 1 == multiply the value to the calculated score and round it down

For instance if you had a limiter of say
Growth = .5
Gain = 0
Strength = 1

When you breed two 10/10/10 chickens, instead you would end up with an egg that has the stats of 5/1/10.