As discussed, for more comparable performance results in T6351 we would like to bypass the Data IO altogether and just provide a filename for the input archive when decrypting and the output archive when encrypting.
Discussed this with werner, this might need a low level adaptation in GPGME because it itself expects a gpgme_data_t and not a filename but otherwise there should be no reason against this. When the output parameter is given it might even clean up a temporary file on error, but it might also not so we should make sure on a higher level that we check for that and remove it when gpgtar crashes or something like that.