Bigger will still play lower, regardless of the room but I wouldn’t get either of those. I’ve had my share of Polk subs including that PSW110 (and its bigger brothers the PSW125 and PSW505) and have no replaced them with a HSU.
Amazon’s listing for the Polk PSW110 claims 23Hz but if you look on Polk’s site, the -3dB number is actually 30Hz. The HSU will go all the way down to 25Hz at -2dB and will have usable output all the way down to the lowest limits of human hearing. Even the PSW505 I have (which is one of the biggest subs Polk has ever made) pales in comparison to my HSU, the Polk is mainly boomy, you’ll hear the bass it puts out but you won’t really feel it. Play the same movie with the HSU and it will rattle your teeth, It actually rattled a ceiling vent to the point that paint was chipping off but that was at really ridiculous volumes.
The best part about the HSU, however, and this cannot be said about the Polk, is that it's also amazing for music. The Polk is, as I said, boomy and never sounds right with music but the HSU is superb. The only sub I've heard that sounds better was a $1000+ Velodyne.