I have a 560 ti in a small form factor case (yeah, I know idiot move on my part) and it's been *okay over the past two summers. But given it's age plus unremoveable dust particulate, I don't think I will be able to use it in this summer's heat.
Is there a GPU of similar (or even less) power that has much better thermal properties?
You could get an aftermarket GPU cooler. The summers in my area would get to ~100F and my GPU would occasionally overheat and auto shutdown unless i ran my fan at 70-80% on the stock EVGA cooler (which also sounded like a jet engine).
I got the Gelid Icy vision that was compatible, unscrewed a few things, put the VRAM heatsinks on with some thermal glue, added new thermal paste to the GPU, and voila. From having to run at 70-80% fan speed with temps while gaming at 80C+, to having the GPU run at 35-40C idle and 50-55C load with the aftermarket cooler. If you are worried about voiding your warranty, you can always put the old cooler back on before you send it in (or in some cases, the company allows you to swap coolers, i.e. evga)