So what's the most cold hardy of the Lime family of citrus? If you answered Persian Lime, you thought what I thought.
Persian lime aka Tahiti lime is good to about 20-22 degrees, and is not quite as cold hardy as a Ponkan tangerine (15-18 degrees) or even a grapefruit (18-21 degrees). It's a green colored fruit outside and traditional yellow-white flesh. Flavor is milder than Key limes, and not quite as tart. I thought it was the most cold hardy variety until I researched Red Limes.
Red Limes are likely a cross between a Rangpur Lime and either a kumquat or a mandarin orange. Expert sources disagree on which one, and documentation seems to be non-existent or lost.
But much to my delight, Red Limes can be grown as far north as zone 8a --- that means 10-15 degrees for mature trees! Red Lime looks like an orange colored lemon or lime shape, fairly large, is deep orange to red on the inside, and actually tastes exactly like you'd expect a lime to taste: somewhat tart, flavorful, and well "lime-y" perfect to flavor punch or drinks. Fruit is quite juicy with few seeds.
Another flavorful lime to consider if you live in zones 10-11 are the Key Limes --- the signature flavor of the now famous Key Lime pies from Key West, FL. But Key Limes are mostly intolerant of frost. In zones 8-9, Key Limes can be container grown in large pots if properly fed frequently and protected from frost when winter arrives. Be sure to take outdoors for UV light during the winter whenever warm weather permits.
And for the adventurous among us, there's Indian Sweet Limes. These are lime flavored, but very low acid and hence the name "Indian Sweet". Indian Sweet is sensitive to frost, but can also be grown in a large patio container if fed properly.
Any of the limes or lemon family of citrus will have multiple crops per year if well fed and protected from cold weather. The more cold weather, the more likely you'll have just one strong crop of fruit and maybe a few more later, as opposed to year around fruit.