I would still argue that it is not so much the maximum temperature that makes Agaves croak out, but more the combination of crazy harsh sun for 8+ hours a day if in full sun and the constant elevated temperature that does not go down very far at night. Last night with the rain was the first time in well over a month we have been below 80F...
The reason I say that, is that everything I have that is under a shade tree or under my shade structures is doing OK to great, most of my potted plants look pretty much fine. Now if I go look at the plants that have limited natural shade or are under limited amounts of shade cloth and that changes, those plants look pretty toasty.
The other issue is that if you buy a plant and plop it in the ground and then expect it to be pretty much OK, you can only expect that to be true-ish if that plant was sitting out in the full sun at the nursery and you are aware of how they cared for it. At most nurseries, things - especially smaller plants - are grown pretty protected, so for full sun planting you really want to go to a place where they grow the plants in full sun, then when you get a plant you want to ask how often they water especially in summer as you may have to approximate pretty closely for at least the first summer as you let the plant settle in and adjust it to your watering schedule.
Even at most nurseries you need to be very aware of the plant source, if plants are imported from California even things listed as 'full sun' will be unhappy in our AZ summer sun (and often beyond), especially if they are young plants any mistake with them can be fatal. Older plants may take much longer to adjust to changed conditions they are usually better equipped to survive a mistake.
Agaves that I have growing in more or less full sun that are OK (they still yellow up in the summer and some still get some protection from the sun with some shade cloth) are:
A. asperrima (gets yellow)
A. americana (variegata)
A. macroacantha (will still get toasty)
A. vilmorriniana (pretty much a champ)
A. sobria (took a few years over covering to adjust, but is still looking good)
A. havardiana (again took some years to adjust, but is only showing some minor yellowing so far this summer)
A. marmorata (will yellow up, but doing reasonably well)
A. weberi (gets very yellow, but with adequate irrigation takes full sun)
A. colorata x bovicornuta (this is a very variable hybrid, the grey colored ones take the sun OK, the green ones not so much)
A. salmiana (some will do great, others take long adjustment)
A. shrevei (very nice blue-grey plants)
A. lurida (complains some but doing pretty good nonetheless)
A. lophantha (very worthwhile plant to grow)
A. ghiesbreghtii (yellows up some but OK)
A. isthmensis (yellows up some but OK)
A. guadalajarana (takes adjustment, but doing OK this summer)
Stuff that needs quite some protection:
A. parryi (with maturity they should adapt OK, but can be very sensitive to over watering)
A. xylonacantha (I have one smaller plant that I got adjusted to full sun, my big mature plant is getting better but has been covered each summer for the last 5 years since planting)
A. parrassana (should adjust to at least part sun with time)
A. victoriae reginae (but I have seen full sun plants in neighbor's yards)
A. nickelsiae (working on getting it adjusted to partial sun)
A. 'Cream Spike' (needs to be moved to very bright shade)
I have a lot more Agaves in pots under 50% shade cloth that will probably be fine, but I have not tested them yet. Like A. cerulata and A. zebra, but again if not adjusted to their new environment in a proper way they'd still burn.
Main thing is that with a month of June like we just had you can expect just about any Agave that sits in full sun to yellow up and start getting some more permanent burn damage on the older leaves even with adequate irrigation. Though adequate irrigation can help avert the worst of that. I simply do not have the time to water more than once a week because I really have too many plants, but if I could I would water twice a week in a month like the June we just had.
