Depends on where you are in zone 8 - that covers a lot of territory :-)) In most cases, barred clematis - those with a darker center marking - tend to bleach out in full sun or lose much of that marking (as well as a washed out flower color). Heat-wise, I doubt you have much of an issue - it's just the sun intensity that may result in flowers looking not as good as the photos.

I love the look of the flower enough that I may risk it and give Empress a try. Wish me luck! I am in Mississippi Zone 8A.

I know a former frequent, much missed poster here, nckvilledudes, who was in the SE US found that the early large-flowered clematis struggled for him, despite his expertise, so you may or may not be successful. There are plenty of folks with hot climates (TX, CA, etc) who do successfully grow early large-flowered types, so I think the only way to find out is to try it. You might want to start out with just one and give it 3 years before deciding if it is happy. If it doesn't work, look at the summer flowering types (hard prune) which seem to be more tolerant of the high humidity/heat combination of the SE.