Penitent engines are random fun up to 3 can occupy a single organisational slot. Hence at 85 points a mini using them in strength can be done. This is needed due to their high target potential and also their unpredictability. The downside of the all metal penitent engine is the work to construct robust mini. If this were not so off putting there could be a horde of up to 9 of these crazed beasts to deliver mayhem across the entire battle field.
Exorcists are more robust but again the random number of shots from these venerable machines can be irritating, and the ability to take several of these 135 point tanks in a squadron would be great. Always add a storm bolter to the Exorcist to give it a little greater survivability, by leaving it with a weapon once the first choice weapon is destroyed by your opponent.
Finally there is the sensible choice with a Retributor squad armed with heavy bolters and mounted in a rhino or Immolator. Sigh