Yes, Dmitry. These have the same meaning always. 'Could' means that the verb is dependant on some whingeing and 'would be able to' is also dependant on something.

"Would be able to" can always be replaced with "could". A native speaker wouldn't construct your sentences. We would initially think that the usage of "could" was a doubtful present "can" and then perhaps have to check your meaning by reading the sentence again. We would probably say something like: a) I would have been finished by next Monday if I hadn't been given that extra work yesterday [third conditional] or b) I could have finished the work by Monday if I didn't have to do so many other things before then. [mixed 3rd and 2nd conditional]