Once the analog signal is converted to a data stream, it IS NO LONGER VHS; it's whatever it has been converted to. VHS has no data rate. Roll your eyes alll you want, it still won't have a data rate.
-DH
You are correct "data rate" does not apply to VHS. I think, maybe what he means is "bandwidth". VHS can have up to about 6 MHz of bandwidth but more likely less than 4 MHz.
Technically speaking "data rate" is rather imprecise and not even a valid unit of measure. I think "Data rate" is a generic term like "length". There are units of length (such as foot, meter or mile) but "length" itself is not a unit. Data rate is a generic term for units such as "bits per second" or "bytes per second". These are all some quantity of data over time. The problem is the VHS is not digital data. There are not bits or bytes. VHS does have frames, fields and scan lines and we can talk about how many of those happen per second (The answer would depend of if the tape were NSTC or PAL.)
When you choose an archive format you want one that will capture ALL the detail on the tape. DV is good at this. Also you want an archive format that will not add any of it's own artifacts to the image. Again DV is good at this.
Also you have to look at the intended use of the archive. Will you want to at some later date edit video or will it only be watched as-is. If the latter DVD is ideal as there are likely to be DVD players around for a long time. But DVD is a poor choise it you want to edit the video. For that DV is good.
No archive format will last forever. Eventually any format will become un-readable. You will need to re-write the archive periodically
And next we can talk about backups. You will need to make several copies and spread them around.