Seeing Comey's smug response following Congressional Hearing and his apparent willingness to return for further questions (no doubt relying on his lawyer to deflect any questions he doesn't want to answer) reminded me of that Q post where he asks whether it is better to declas before or after.
The answer is neither. The best time would be between hearings, with a non-publicised declas made available to the Committee. Let him return, confident and smug in his/his lawyer's ability to deflect awkward questions, only to be faced with declassified, documentary evidence.