Long blooming red is hard to find, at least it is here in zone 4. You are almost best to use a number of reds to cover the season. Monarda is good in mid summer, lilies also, Helenium comes in good reds for later summer,cardinal flowers if you have the right soil conditions... My best long blooming red is Knautia Macedonia, it is not a bright red, more burgundy (purplish in cooler weather)...I don't know if coreopsis "Limerock Ruby" is perennial in your zone, but if it is, then that would be a good choice too.

This is Polygonum persicaria, commonly called Knotweed, Smartweed, or Lady's Thumb. It is native to Europe and considered an invasive species here. (I just looked it up so don't be too impressed!) I've actually been using these plants to fill space in my big new flowerbed for a couple of years. I pull all but 3 or so. They are almost 6 feet tall right now and about 8 feet around. The stems of some of them are bright red and very pretty. The only thing is trying to decide when to cut them all down to prevent a million little babies next year. I let one go to seed in a corner of my vegetable bed last year and this spring I literally had a carpet of little baby plants, and they germinated in succession. I pulled babies for a couple of weeks and they just kept coming. I ended up just spraying them all with roundup. If you can control its potential to take over, I think it's a really beautiful plant.

I am very familiar with most common lychnis forms, the flowers are pretty much forget me not looking (or brunnera) in upright clusters with rounded pea shaped buds (like a loose broccoli head) and they are a muddy muted terracotta leaning towards the purple side ( not neon or tomato red). Maybe I'll have to take a pic so I can research it. They really are quite odd looking but I do have a tendency to collect oddball plants.

Lantana New Gold (I think thats the name) is reliably hardy here in Oklahoma zone7b and after living in North Carolina, I can tell you our winters are worse than yours. I've had one in the same spot for about 6 years now. It gets about a foot and a half tall and spreads out very wide but can be trimmed back. Miss Huff is a more upright type that is yellow, red and orange, it gets pretty big and needs some space. Its a heavy bloomer and touted to be the most cold hardy. I've also got a heavy blooming solid orange type that is winter hardy but I don't know the name of it. Agastache doesn't do well here in spite of good drainage on a slope in sandy soil, either the humidity gets it or a rainy spell will do it in. I finally gave up trying.