Whether 75 is all that warm depends on the humidity. I think doubles are the way to go, if possible.
Nope it's really a combination of things, that depends mostly on the altitude of the Sun, then the humidity. 75/humid in the early morning or evening is easier on you than 75/dry with the Sun beating down on you mid afternoon.
Malmo, you are by far one of my favorite posters on this board but you are 1000% wrong on this one. 75/muggy in the morning feels much worse than 75/dry. I've lived my entire life in the deep south (MS, LA) and can assure you that the locals would LOVE to have 75/dry with or without the sun beating down on us in mid-July. That's an extremely comfortably cool day in the summer for us and in most places would probably be close to a record low in the middle of July or August (the two worst months).
OP: I know everyone says deep south broadly, but the weather is a bit different in east Tennessee and western Carolinas than it is in Mississippi, Texas, Louisiana and Georgia. Either way, it's hot as fire between late June and late September. It's simple as running early in the morning and late in the evening. Run doubles. Whether it's 15 degrees in the winter or 95-105 in the dead middle of summer (trust me, it's the closest to hell as you can get), doubles are always great. For long runs, you will have to stop every now and then and drink some fluids. If you can, run loops where you can stop at the same spot and drink something. What has always helped me during long runs is grabbing a handful of ice cubes as I'm leaving my water break. Just take the ice and rub it all over your body until it melts away (including legs, but focus on core and head). Drink more water throughout the day, take cold showers, eat more citrus fruits, and wear lots of water resistant sun screen. And yes, Black people need sun screen too:)