I usually see mine start to look a little stressed when temps are in the 90s, but they come back when given water. I also think its according to the type of banana.
I find that bananas love heat (but a humid heat, not a dry one), sun (when its cooler, but maybe some light shade in very hot climates, and water(only when its warm, they hate water in cooler weather when day temps are below 55-60F).

Good luck!

I had read somewhere that optimum temperature for most bananas is 84-92, growth slows above 92, and stops altogether at 98-100.

That cement wall might make a big difference. I wondered why an orange tree I had was cooking when it was 98-100 outside, until I put a probe out there and saw that the brick deck it was sitting on heated the tree to 115.

Dry will certainly be bad, but everything I know about Nicaragua says it is pretty much jungle-like humidity so I'm guessing that isn't a problem for you.

Well, along the Pacific Coast of Nicaragua (where I am) there is a rainy and dry season. During the dry season, there are 6 months of NO RAIN at all. As you can imagine, high temperatues, a direct sun angle and srtong winds take a toll on bananas. Most of the "wild" bananas are totally fried by this time of year, they literally dry up.

The dewpoint is usually around 60 here, even in the dry season, but still, if there is no natural rain, the banana plants tend to suffer.

I have been giving them good waterings and I cut them off and now some tiny pups are comming up. I left all of the orignal stalk and leaves as muulch so there is shade for the ground and nutrients to break down. They also keep the soil moist and cooler.

I can tell you that here the temperatures reach 100 daily and the plants keep growing as long as they get watered. Remember that it may hit 100 for a couple of hours, but then it cools off.

I get the feeling though that the cement wall makes it worse, plus the bananas went several months witouth watering due to a water shortage, so they are recovering slowly.

If I get an established grove, that is more sustainable and they are happier in clumps, which is my ultimate goal. But boy they sure so need a ton of water...

I have tried to figure out the amount of water for my bananas, and it seems like the more the better.
One thing to consider is your drainage. When I plant a banana, I make the hole 2 to 3 feet in diameter, and at least 2 feet deep. I then fill the hole with water, and see how long it takes to empty. If it empties in a couple hours, that's good. I then take top soil, dried horse poop and sawdust mixed together in to fill the hole. I then build a berm around the hole to hold the water.
I made a planter 12 feet in diameter, and went down six feet before I was satisfied. I planted, I think, four bananas in it, and three years later now, I have over 30 trees growing in it.