Is a 23x16 room too big for B&W 805S bookshelfs?

I usually listen at about 80dba.

The effects or contribution of a sub in a large space will be relatively small. Setup and sitting arrangement are crucial in this circumstance. Listening distance from speakers preferably not more than 8' or you would lose the scale, enveloping sound and bass slam from the 805S ie. the whack of drums and the surreal feel of live dynamic music. A larger full-range floorstander will perform better but the 805S can sound decent if listening in near to mid-field arrangement.

Hmm... I absolutely love my current setup. Maybe it's time to step up to the 802Ds of the same series? Has anyone compared them to the 805S? Obviously there's going to be more bass, but what about the highs, mids, and everything else?

Yes they are too small, the bass will be very weak. If you plan to sit near field you will be fine.