I think I figured it out. Apparently the potion_of_power_l4 has cumulative permanent effects.
I had my character drink all five remaining potions, travelled for three days, then rested. I fought the Temple Guards again with this result:
Garris crits Skaen Temple Guard for 335 Pierce damage.
Acc:439 – Def.:67 = 372. Roll:22 + 372 = 394 (Crit). 30.1 – DR:9.0 = 21.1 Pierce + 308.2 Slash + 5.3 Shock.
I guess that's the risk of using the console. Is this fixable, or will I just need to start a new game?