My red sex-link laid daily through our 104 degree heat wave of last year. I had a fan on them and gave them plenty of water but she did just fine. My black sex-links aren't the layers the red is. They're bigger birds, too, and they didn't handle the heat as well. Maybe it's just the type I got but I prefer the red for laying.
That being said - it's my understanding that red and black sex-links don't lay as long as other breeds and that they "burn out" in about 2 years. I wasn't aware of that when I got mine so I'm adding other breeds this year in anticipation of them slowing down in about a year.
From what I have read, chickens can all lay about the same amount of eggs over their lifespan. Being that Red sex links can lay 300-340 eggs each year for their first two years of laying, I would expect them to hit that ceiling faster than other breeds.
Our Red Star has earned her chicken retirement, we will keep her until she passes. She is amazing and out of our original 9 hens her and one other are the only ones we have kept. We sold the rest and replaced them as they got older. She is now over 2.5 years old and is laying an absolutely huge egg 6 out of 7 days or more each week.