Again, I am not an expert on aircraft capability. I only know of various aircrafts and some of there fights and actual flights. Stuff from the Histroy channel and stuff. Also some videos on specific aircrafts.
1.) HEAT The Sahara is not any hotter than many other regions that run along the tropic of cancer which is the hottest region in general across the globe due to the angle in which the sun rays hits it during the Northern Hemispheres summer, or the tropic of capicorn during the Southern Hemispheres summer. As a vetern of Iraq, I will tell you that I was in a maximum of 140 degree heat with kevalar, body armor thicker and heavier than anything in world war 2 and sat in an all metal humvee. I am sure the aircraft of the day had air conditioning due to the fragile instruments. If it didn’t, there are many other regions just as hot that does not have unpassable regions.
2.) I have a lot of experience having to due a lot of maintanence of equipement due to sand. But sandstorms on the the ground. They cover some sky, but common, “have I heard”, how about you obviously have not heard. Sand storms are not as bad 20,000 feet or so in the air. Again, I have no idea at this point how high the normal fighters of the day flew but the premise of my discussion was to find out something new from someone I may be overlooking, not something off the top of your head that seems to make some sense.