Potential issues letting the Polks run full range would be:
a) slightly higher IM distortion (only really an issue if you're blasting it)
b)the Polks are bass reflex alignment, so they will exhibit a considerable phase shift at the lower extremities of their response, which can be problematic when it comes to blending in the subs.
Your room is very much more of an issue at these frequencies, so running the sub with a bit of overlap with mains running full range can actually help with modal smoothing.