It may be overkill, but it's an archive. Overkill is permissible.
Remember, there's no going back to do it again -- once the video is digitized, the tapes will go away forever.
That said, I think a bitrate of about 0.78GB/hr may be better. It may still be overkill, but will let a T120 tape recorded in SLP mode (6 hours) to fit into one single-layer M-Disc DVD-R, which may make sense for some media.
But whatever the case, bits are cheap these days. Data storage is definitely the least expensive part of any operation like this and it tends to get cheaper over time.
The most expensive part of things like this is the time it takes to make it happen, and bitrate (whether high or low) doesn't have a substantial impact on that time.
