For k a field of arbitrary characteristic, and R a k-algebra, we show that the PI degree of an iterated skew polynomial ring R[x 1 ; τ 1 , δ 1 ] · · · [x n ; τ n , δ n ] agrees with the PI degree of R[x 1 ; τ 1 ] · · · [x n ; τ n ] when each (τ i , δ i ) satisfies a q i -skew relation for q i ∈ k × and extends to a higher q i -skew τ i -derivation. We confirm the quantum Gel'fand-Kirillov conjecture for various quantized coordinate rings, and calculate their PI degrees. We extend these results to completely prime factor algebras.