I did buy a D4, and just shot it out with my m88 on my own bass drum (Rogers XP-8.) The mics were about a inch outside the resonant head vent.
Different voicing, no doubt. The D4 doesn't go as low as the m88, and has more top to it. However, the D4 has a bit of slap built into it that I like. Not a scooped sound like the D6, but, on my kick, an easy choice for live, when you not working with gates.
I'll be using it tonight for a live performance (my own.)