... or just be fast. With my berserker, slap on the Boots of Speed, drink Oil of Speed (very good speed aftert that!), use Draw Holy Might (or whatever the special ability is) and charge heh. Target Illithids first. I went through the first Illithis place (with the Hammer of Thunderbolts) very fast. Gotta keep the eye on the INT though, I had 1 left when I killed the last one heheh.. Close call. There are potions which raise the INT, one raises INT and DEX. I suppose they should stack, so even better - get +7 to INT and +3 to DEX, and then charge the room
And, there is no resistance against it as such. What I don't know, have not tried, is whether the Restoration, or Lesser Restoration, would restore the INT. In a way, it's drain like any other there is. Maybe it works and could help, though you would need to rest after the battle, since restoration drains the juices..