There is no way players who take a more cerebral approach to the game of D&D can RP a low intelligence char. The amount of actors in a D&D game who can act as well as Penn or Malkovich (who played roles with mentally deficient chars) is few and far between. Now, those actors portrayed chars that were well below an 8 in D&D terms. But I never see the smarter players at a table backing off their RL intelligence when it comes to groups formulating plans inside a game.
And inside the group at my gaming cafe, the chars that try to play low Wis chars, typically Chaotic Neutral chars, who rush speak before thinking, or rushing into insane situations, the well-known term of "Chaotic Stupid" is used.
The only true measure for those stats are not with RP, but inside Ability Checks and Savings Throws, which opens up the entire can of worms where a char that might have horrible decision-making skills and considered low Wis might also be great with Animals, or any other number of combinations that don't make sense.
Bottom line, trying to RP any ability, especially the soft ones, is pretty much impossible except for the most skilled actors.