I just had a 5 head Seagate drive where I was able to read 4 of the heads at about 100MB/second and head 1 was reading at least than 100KB/second, but reading most sectors. Rather than wait months to clone the one head, I changed the heads and got the drive clone completed with a couple hours...the drive fully cloned with no bad sectors.
Nice to give our client good news about a successful recovery.