I have the stock ALH cooler and hot weather really takes it toll on power (or so it seems)
I think hot intake air is a bigger drag on summer performance, as it reduces the effectiveness of the intercooler. During Formula 1 broadcasts on Speed, when they give air temps of 80-85°F, typically the track temps are 115-120°. On a hot highway, in mid-day in the South, with air temps of 105-115°, road temperatures could reach 140-160°.
That heat, radiating off the asphalt, must have a greater effect on combustion efficiency than the few degrees' change in fuel temperatures.
Additionally, if the fuel temperatures are already ~110° when you start your trip, you would have to travel several hours before the fuel temp would climb much higher. The best you can hope for with a fuel cooler would be to keep the fuel from getting much hotter than 110°. But the air temps would affect performance no matter how far or how long you drive. And the air temps would limit the effectiveness of a fuel cooler, too.
Thus, it would seem to me that a fuel cooler can have only limited effectiveness, even in the most extreme conditions. And even less effectiveness in more temperate climate zones. The only exception would be if you plan to drive several hours at a stretch, during which time the hot fuel being returned to the tank could raise the temperatures there by many degrees.