Slackware :: Search Harddrive For MBR Backup?

I screwed up and managed to overwrite my MBR with one that had a different partition table, thereby losing access to all of my partitions and data. Now, I was semi-smart and backed up the MBR before I did this, but the "semi-" part is that I backed it up onto the hard drive in question because I was thinking only in terms of losing my ability to boot from the MBR, not the whole partition table.

So...as I see it my only means to recover my data is to find and recover that 512 byte block on the disk media. Having read a little bit, this seems possible given that I know to look for a) the MBR signature at offset 510, b) the partition status byte at offset 446, and c) the partition type byte at offset 450.

What I need is help figuring out the most efficient way to do this. I've experimented with a shell script using dd, hexdump, and grep, but searching 1000 blocks takes ~20seconds, so to search the whole drive (100GB) will take something like 800hrs. This is limited, I believe, by the fact that my live disk of Knoppix won't recognize a drive on the SATA bus, so I had the target drive mounted through a USB adapter. But even if it were being accessed via SATA, I have a feeling it would be pretty slow.

I need someone who is an expert to help me figure out a script, program, etc. that can search for and identify the sector where my MBR backup resides more efficiently.