There's not all that many types of evergreen clematis, so if you want to go evergreen, that'll limit your choices. C. armandii is the most common one and is a big, robust vine that will cover a lot of territory - 30-35' is not unusual for a well established vine. It's also hardy for your area but I'm not sure how well it responds to your heat. Maybe Jeanne will chime in with her experiences :-))

$55 is a reasonable price for a 5gal armandii here, but gallons should be available as well for somewhere about half that price or a bit less. C. x cartmanii hybrids are also evergreen and offer a very interesting, heavily dissected leaf but these are not viners but smaller sized, sprawling selections. It would take a good number of these to fill up a fence line! Both are early spring bloomers with white flowers (or with armandii 'Appleblossom', very pale pink blossoms). Armandii is also fragrant and here in the PNW, will often have a smaller, repeat autumn bloom.

I would not recommend planting evergreen and non-evergreen forms together unless you space them out considerably. The evergreens do not require pruning and the aggressive growth habit of armandii will easily overwhelm the smaller selections of LFH's if they are anywhere within its spread. You could always choose a selection of the LFH's for a wide range of colors and extended bloom times but there will be a period during late fall to early spring when the vines won't look very appealing.

Ditto to what gardengal said--the evergreen armandii can get quite large and typically doesn't need pruning. At my previous house, I had armandii and it could get scraggly looking in the winter as the winter winds burnt the leaves and quite a few would blow off. In that case, I did prune the plant back to stimulate more growth and to get the plant to fill in.

If it were me and I had such a large fence to cover I would go for the type IIIs. The type IIs in my zone get quite ugly looking in the middle of summer when they tend to brown out. The type IIIs could get trimmed back when they get crispy and will rebloom for you in the fall.

Any clematis you plant isn't going to look that great during winter and like was previously said the Evergreens will just have blooms in Spring..Whatever you decide to do sticking with the same pruning group is advised or you'd have a nightmare..the Montana's are pruning group 1's and only bloom in spring as well..Like gardengal said they can get huge!!..Sweet Autumn clematis is another than is hardpruned and grows to be big and then will bloom in September here..I like the idea of pruning group 3's myself Jeanne