Not zone 5 but I know several people that grow some of the floridas in zone 5 here in the US. The thing is that the only way you will find out if they will survive in your garden is to try it. You could have two people in zone 5 who have extremely different growing conditions and temperature swings. All that zonal information gives you is the average highs and lows, and nothing about humidity levels, temp swings, rainfall, etc.

I like Ellen Horning's spin on the whole zone misconception. The following is something she has on her Seneca Hills Perennials website and to me it spells it out best:

"Plant hardiness
We can repeat this rant until we're blue in the face: hardiness zones do not tell you most of what you need to know to grow many plants. For example, Syracuse, New York and Omaha, Nebraska, are both in zone 5. Do you really think their growing conditions are similar? Of course not. The totality of the growing climate, not just the winter low temperature, affects the plant's performance. Snow cover, soil type, presence of pathogens and predators, patterns of temperature change, patterns and amounts of rainfall, drainage, and other things all matter. Is there any simple way to summarize growing conditions? No. A good gardener experiments. A good gardener kills a lot of plants. A good gardener is not literal-minded about hardiness zones, either way.

To complicate matters, when you attempt to grow plants from ecosystems very different from your own (some of our South Africans, for example), it may be impossible to predict whether they will do well for you, because too little is known about their cultural requirements. Oswego does not much resemble the Drakensberg, but a lot of Drakensberg natives seem to like Oswego. Why? We aren't sure. Maybe we just have a magical mix of conditions. Doubtless you too have a magical mix of conditions, but perhaps it suits a different set of plants. You must be willing to experiment, because we simply cannot tell you whether any given plant will do well for you.

The bottom line here is that we include hardiness zones largely to pander to popular prejudice and give you a small degree of guidance. The fact that your zone number is equal to or lower than the one given for a particular plant must not be construed as an assurance that this plant will grow for you."

USDA hardiness zones are also very misleading because they don't take sun and heat into account.

There is a huge difference between zone 8 in Portland OR and zone 8 in the SE. We have grey skies and only a few days over 80* and the SE US may have over 100 days over 80*

Out west, Sunset Magazine has much more accurate zones.