Without buffs? I'm... pretty sure that's impossible. Personally I've got Adell with a weapon proficiency of 255 for fists, 25 Lovers, a perfected Ultimus, three perfected Super Robo Suits, all with maxed out SPD on top of the fact that this was the stat I maxed out for him during his final reincarnation... And I still haven't been able to get it any higher than 18 million. Admittedly I have yet to fill all those items with as many maxed out Coaches/Sprinters as I possibly can, which might push it over 20 million, but in order to reach the cap, I'm pretty sure you need to use stat-boosting spells.
However, I have seen videos indicating that Magic Knights don't actually need more than 20 million INT to completely obliterate even the maxed out Pringer X'es. As long as one has sufficiently high stat-mastery for all the elemental spells and maxed out elemental affinity using the Specialists that boost that, just gathering all eight Pringers into one cluster and bombarding them all with a Peta-level elemental spell or two should be quite sufficient to win.