I've done both the Clark Liver Flush & pancha bhoota. Typically I take the castor oil/oj mixture with a teaspoon of Epsom Salts & a teaspoon of cayenne. You're correct in that their results are similar, however pancha bhoota is touted as a bowel flush...perhaps it would be a worthy addition a couple of days AFTER a Liver Flush in order to expel any stones that may have gotten caught in the bowel.
How does castor oil 'compare' to olive oil? It depends on its application. Castor oil is particularly suited for oil pulling, detoxing thru packs, etc., whereas olive oil is more nourishing and more of an adjunct to the daily diet.