I would expect the thermals to rise much higher over the Saudi desert where there is little humidity to condense and stop the rise.
I found that true over our southwestern desert.
My normal cruise when there were no wind or clouds to influence my choice was always 7 to 10 thousand feet. Generally more pleasant up there, and a maximum amount of time to troubleshoot a problem, or find a good place to land. Maximum range for the radio calls too. I live at sea level, but am active, and never had any oxygen problems.