Define bass slam? I don't know. Something I can feel with my body. Thump, slam, shockwave, etc
If you are looking for high impact shockwave rather than resonant or warm muddy or dull but impressive bass - i.e. you want short duration but something that hits very hard so you feel rather than only hear it - then look at "critically damped designs" with pro woofers of 8" or more.
JBL's. Tannoys. ATC etc.
For example a pair of Genelec 8050A new (including built in amps) will set you back about $4500...and give plenty of SLAM in a medium sized space. I would say 8" is a minimum as few six inchers have much slam and two six inch woofers rarely equals an single 8 inch. Also be wary of ported designs if the port is designed to give the speaker bass extension...good luck!
I think you may find the Mahlers will be in the warm but impressive direction rather than pure "slam" or tight bass. Of course, I may have misinterpreted your meaning of "slam"...