For me it has survived the last two winters, but it has not 'thrived'. Is it less hardy?- I don't think so.

In zone 7b, I've found 'Santa Barbara' to be MORE winter hardy than the parent species!!

One trick with S. leucantha in the northern reaches of its winter hardiness ranges is to make sure it is planted immediately after the last frost date so it has a full growing season to establish before encountering its first winter. This is particularly important in clay soils since the new roots will have a tendency to remain in the more friable old-container soil ball rather than easily go into clay (especially if it is dry and a bit hard)!

Oh yeah, the dried stems should be left on the frost-killed plant over the winter, this tends to protect the root crown better. This is mainly important in zones 8a, 7b, etc but not further south in milder winters.

Here is a link that might be useful: Santa Barbara Mexican sage