We are in NC and have the same hot summer you do, altho yours gets hotter. We've only had our Optima for 3 days, but we learned fast the first day to not set that heater above 94. We find 94-96 a perfect temp for us, day or night. We put up a canvas gazebo (free Harris Teeter giveaway!) over the spa to block the sun this summer, that helps it not heat up w/out the heater on. Ours is set to 95 and its been at 96 for 1-1/2days now, steady. At 94-96degrees, we can stay in for 1-2hrs and never feel overheated.
A trick you can do day or night if its humid and hot but you still want to be in tub: buy a hose nozzle with a misting setting (Rainbird makes one for $10 @ Lowes with 5 settings) rig up your garden hose to hang over your spa if you can and set it to mist down on yall, that will keep the bugs away and the cool water will keep you all cooler and actually make the hot water feel nice. It also cools your spa down by adding some cold water.
