To simplify the expressions, we will apply the rules of exponents:

(5p^4q^2)^3 / (10pq)^2
= 5^3 p^(43) q^(23) / 10^2 p^2 q^2
= 125 p^12 q^6 / 100 p^2 q^2
= 1.25 p^10 q^4

8xy^2z^4 / (1.6y^2z)
= 8x y^2 z^4 / 1.6y^2z
= 8x y^(2-2) z^(4-1)
= 8x y^0 z^3
= 8x * z^3

Therefore, the simplified expressions are:

(5p^4q^2)^3 / (10pq)^2 = 1.25 p^10 q^48xy^2z^4 / (1.6y^2z) = 8x * z^3