Did you upgrade it to the Fido?
Tried both the modded K9000 and the fido. The K9000 modded with the Mentat Chow mod does more damage per second than the FIDO.
But they were doing less damage in VATS than my AER14 prototype. One full bar of APs frequently wasn't enough to kill one enemy.
With the AER14 I get more frequent crits, plus added damage and stuff from perks and that KABOOM effect from the Meltdown perk.