Participles behave much like adjectives. Do they also have comparative and superlative forms? They are easy enough to form: ferentior, dicturissimus.
More precisely, are any comparatives or superlatives of participles attested in classical Latin literature? Some participles have started a new life as independent adjectives. I prefer to leave participles that are often used as adjectives out — if the distinction is sensible. One could argue that comparison always requires treating a participle as an adjective, but I would prefer to see cases where this treatment is ad hoc rather than widespread. I leave it to you to judge what counts as adjective and what as participle; I hope the intent of my question is clear enough.
I can fathom use contexts for compared participles. Using my two examples from above, I might want to describe someone who carries more cargo than his friend or someone who is going to give an awfully long speech.
(I had used latus as an example of a participle which has become an adjective, bud fdb indicated in a comment that they are in fact etymologically separate words.)