Not sure how I missed this tread originally, but 60g of beans in my french press most days (for the 32oz bodum press). Some days I’ll do 2 or 3 2-shot-lattes. Or else 1 or 2 cups in a v60 (accidentally bought a 5lb bag of preground and my jura really doesn’t like it). Add in a diet coke or maybe a green tea, now that it’s winter. It takes at least 2 more cups of coffee for the jitters to set in, and I prefer to avoid that feeling.
Caffeine tolerance varies to a much larger extent than is commonly understood. Caffeine works in your body the same as many other drugs/substances (not meaning “drugs” as in illicit substances, but anything else like Tylenol or your usual blood pressure medicine) in that it is broken down and deactivated by your liver. This rate is determined by ratios of specific liver enzymes, which in turn is determined by genetics and random variation.
These variations can be massive. For my N=1, I had trouble falling asleep for years, and when I did sleep, I was a “light sleeper,” and would wake up to any tiny little thing, and sometimes to nothing at all. Then I would struggle for an hour or so to fall back asleep. I obeyed all the sleep hygiene recommendations religiously, including no caffeine after noon - still didn’t help. I finally decided to bite the bullet after years of misery trying to fall asleep, and I cut caffeine all the way down to only coffee in the morning, then only 6 oz of drip coffee with breakfast. The difference was astounding. I now sleep much better. This is in contrast with my roommate who could drink espresso all day and have a cup of coffee right before bed, then sleep like a baby.
Caffeine limit recommendations are based on the bell-curve of liver enzyme clearance rates for the general population, but know that huge variation exists. You might be someone who clears it very slowly, and even a small amount of caffeine in the mornings is leading to significant accumulation in your system. You might not be getting all of the serious toxicity symptoms (tachycardia, hypertension, palpitations, anxiety, sweating, etc) but still get terrible sleep effects.
Michael Pollan has a super-interesting Amazon book thingy on caffeine, highly recommended. There are also numerous medical resources describing the variation and signs/sx of toxicity.