How much does heat effect 5k time

Yes, 95 degree temperatures affect a 5K, but the amount varies greatly by individual. What was the dew point?

Not as much as it affects it

It was mostly super dry out I remember not being able to swallow after the first 400m.

40 seconds is a lot. If you ran 16:20 I would say yes it was probably a sub 16 race. You probably ran a 16:20ish equivalent today.

Where do you live that it's that hot in November?

San Diego, California

I would be happy with a 16:20 because that would be a PR from stanford invitational earlier this year. Our home course is much harder than stanford.

I ran a 5k in Texas on July 4th and it was over 100 at the start. I was running at half-marathon pace (6:05/mile) and it felt like the hardest 5k I've ever done. I'm also 6'3" 180lbs so heat effects me significantly. In 50 degree weather my pace is in the 5:30s. So, in my experience, yes, heat significantly effects your 5k time, especially when it's in the 90+ territory.