Hypex Ncore technology has really upped the performance standard for Class D. I have a pair of monoblocks for sale right now here on Audiogon if you're interested.
But I would caution that amp power, while important to deliver slam, is not the only precondition. You also need clean and dynamic source electronics capable of driving the amps well. Since slam is about dynamics, if you don't have high resolution and low noise signal, it will blur the dynamics and detract from the slam. We are always fighting some level of dynamic constriction in recordings, some worse than others with the loudness wars, but even really well recorded stuff is much less dynamic than real life. Such is the nature of recording vs live. In order to maximize dynamics, the entire signal chain needs to be clean and clear, and electronics need to have good impedance matching with each other so they aren't strained and have enough "drive" to create that realistic slam. A good preamp is often key to giving that last bit of drive and dynamics to the music.
I also think clean power into all electronics is highly critical. Good in restrictive power conditioning like the Pi Audio units and power cables that do a good job of rejecting and filtering noise can really reduce the noise floor of your system, which in turn increases dynamic contrasts and slam. Of course it also greatly improves imaging, soundstage, and micro dynamics as well, so it's not either/or when it comes to slam and other audiophile characteristics.
Finally, I would say proper management of bass resonance and nulls in your room are vital to slam in the bass frequencies. Untreated rooms are a horror show of bass anomalies that produces varying levels of boom and suck out at different frequencies. If you can use room treatment, multiple subs in a distributed array, EQ, and/ or combinations of these to even out the room response, your system will be capable of producing clean and even bass that will then slam rather than booming.
