Mitch: I think if you live in a dry heat sensitive area, using larger pots will always help you with the heat. I also think that due to climate change and hotter summers for many, that the addition of shade cloth is going to become more common. I lost all of my tomato plants this year, and I'm on a quest myself to prevent it next year.
I live in the desert where temperatures average between 103 - 110 for three months straight. I learned early on that smaller pots were useless here. Between the dry air, wind and heat , a pot less than 10 gal. will dry out faster than you can turn around. The larger pot retains more water and keeps the roots from frying in the heated soil. Your situation is not as bad there, but the same principal still applies.
MarianneW: What are you growing in the shade there? Do you mean real 100% shade or filtered shade with a shade cloth or tree?
Have you been successful in growing any
good tasting heirlooms there? (Cherokee Purple etc.) I hate when the question is asked what can you grow in the hot desert and people either say "cherry tomatoes" (I hate cherry tomatoes) or some god awful tasting heat tolerant tomatoes that taste no better than store bought tomatoes. Why in the world would I want to go through all of this work to grow Homestead or Yellow Pear that tastes like wet rubber. .
