Best new or used speakers for under 3K?

Easy.... Boston Acoustics E-100's. Killer sounding (and looking)
speakers no body knows about. Not much out there on
them, but they were a statement speaker for Boston,
that I guess just did not sale.
But for reference, I had the Def Tech Mythos STS's and
ST's right before these, and IMO there is no comparison.
$2700 (with bases) through Amazon.

After looking again at your room size, the Bostons
may be a bit to large!? They stand 6'5" tall. BUT they
also can be wall mounted if that is an option for you.
Then they are only $2500 (shipped) without bases.

For a room that size, I would think a small floor stander or a larger stand mount speaker would suffice. Under 3K and with the power you are going to have on hand, I suggest:

small towers

EPOS M16i
Totem Hawk
Quad 21L2 or 22L2
Devore Gibbon 8
Focal Chorus 816V or 826V
PSB Imagine T
B&W CM7

Monitors

Usher Be-718
PSB Synchrony Two B (why not?)
Dynaudio Focus 140
Aeriel Acoustics 5B
Revel Performa M22
Totem Model One Signature

Save up an extra $500 and get the Zu Essence. One of the better sounds at RMAF.

I would also consider a trial of the Ohm Acoustics Walsh 1000s. Assuming an 8' ceiling, this is the appropriate model for your room. I am just at the end of my 4-month in-home trial on a pair of the 2000s (also within your budget, but not necessary). You can check out this unsual design at ohmspeakers.com. The entire Walsh series sounds very similar, with the design scaled for different room volumes. Breifly, I have found these speakers to excel in many areas, especially timbre, freedom from congestion, detail reproduction, soundstage width and freedom from glare and grain. Excellent customer service, and designed and built in the U.S.A. Also, see the thread "Ohm Walsh Micro Talls: who's actually heard 'em?" in the speaker forum. (I have no affiliation with Ohm Acoustics).