What is under $5k speaker with best bass slam?

I can't resist chiming in in favor of Mahlers. Indeed they can exhibit definite 'bass slam'. Furthermore, unless they are set up properly, they are driven with a great deal of power and a stout damping factor, they can in fact exhibit an excess in the mid to upper bass and some undue warming in the midrange. I have now used Mahlers for 6 months and have driven them with legacy Rowland 7Ms, Nuforce Ref 9 SE2 and Rowland 312. The only configuration where I may have detected some traces of unwanted stereotypical behavior is with the old 7M monos. With the Rowland 312 and Nuforce there is no bloat anywhere and bass is strong and instantaneous, if perhaps slightly more musical and pitched with the JRDG 312. It is worth pointing out that in rooms that tend to suffer of runaway bass, configuring the Mahlers with the subwoofers firing inward may yield a tighter -- if perhaps less expansive -- bass response. Lastly, my Mahlers started to sing only after a 500 hrs breakin followed by a professional 'Master Set' performed by Soundings of Denver (Co). The Mahlers have been just updated with a new tweeter configuration and are now on version V1.5 which has unfortunately gone up in price. Used Mahlers on the Gon are therefore an absolute steal!

Powered Sub (JL Audio) if you want to be able to feel bass slam at low volume, and you can adjust the slam as feel the need!

Try the MFSL OML-2.

You might want to look at the Ariels, maybe a used 10T.

And aren't NHT speakers known for bass 'slam?'