I've given S. greggii hybrids a couple of tries here in the northern part of zone 6, and had none overwinter, though I've gotten other supposedly tender Salvias to make it for at least a few seasons. High Country Gardens has a lot of interesting stuff potentially worth experimenting with, but in general I'd add at least a zone to their projected hardiness ratings (i.e. with plants they describe as hardy to zone 5, I'd expect survival only in zone 6 or above as a general rule). Prolonged cold wet weather in the Midwest and Northeast and damp winter soils are tougher on perennial survival than the conditions which apparently prevail in much of the Rocky Mountain West.

Mine are in a south facing bed that has a garage wall on the north and west side but they are in the east/south part of the bed. It has some overhang of sparse oak branches that have no leaves in Winter and they have survived 24* weather for a couple of days. I mulched with redwood mulch - real hairy like. I used small stones and redwood mulch on my other tender Salvias and they all came back except the Leucantha.This is a fabulous Salvia - I call it the "Energizer Bunny" as it blooms for so long. Be careful as the branches are brittle and easily broken, otherwise enjoy.

There is little doubt in my mind that the cultivar is extremely hardy. In past several years I've grown it in several gardens in zone 6b and 7a. It is one of the greggii that doesn't die to the ground. This last winter a truck drove over a dozen of them in January and despite the abuse all but one of the plants recovered. If yours are growing in a really dry site you might consider planting very deep. The buried stems should root at various levels underground and that might increase the chances of something surviving. If it survives the winter I'd love to hear about it.

I agree, San Carlos Festival is the oldest microphylla in my garden, surviving in a bed where at least a dozen other microphylla and greggii cultivars failed to thrive. The only place it did not do well was when planted in totally barren dry conditions. It doesn't set lots of seed for me either, although it was a parent of one of the most vigorous and hardy seedlings ever to appear here. I never know what to expect from new seedlings and that includes flower color, leaf type, hardiness or vigor. Most of them are so similar to the general profile of the sister species as to be unexceptional - shades of raspberry, red, or pink. I keep asking myself how Robin comes up with so many beauties.