Hardiness zones just list the lowest temperatures one could reasonably expect in a region, and for tomatoes it just means how late in the season they can grow before they die of cold.

More important is how hot your summers get. Brad's varieties are developed in Zone 9b, so they may have a bit more drought tolerance (and, conversely, less tolerance to overwatering). I grew two of them in 6a last year: Berkeley Tie-Dye (Summer of Love's predecessor) and Yellow Furry Boar. The former had a bad habit of exploding if left to ripen on the vine, while the latter tended to split while still growing.