I think moderate consumption is a function of tolerance and the specific metabolism of the person combined. I remember reading a comment in HN, where the commenter had a genetic trait which slowed caffeine metabolism by 4 times. So, he had it inside his system 4 times longer, and caffeine had no positive effect on him. However, let's not digress.
I'm not a body hacker, and I don't like to mess with my body much, however I had limited time, this was once in a lifetime situation, so I had to put some regular hours to finish my Ph.D. corrections.
Also, it's worth noting that I'm an avid black tea drinker since 6 or so. I didn't change my tea consumption habits through my life.
First, I read about resetting caffeine resistance/dependence. The method is simple and clear: "Give up coffee for a week. You'll have headaches in day 3-4. Endure. You'll be fine". Then I started to consume coffee to the point where I felt productive, yet not tipsy. I have a Starbucks mug, it's "Tall" in Starbucks parlance. I started with two cups. One morning, one after lunch. As the resistance built up, I started to increase in a controlled manner, to the same line. Productive, but not tipsy. I was putting 10-12 Pomodoros a day (250+ minutes of truly deep work), and my mind was mushy and tired everyday at ~5PM. I never pushed my body beyond that point, because I needed that brain tomorrow. Left my desk and got rest.
I finished everything on time, left coffee for ~3 months, had the headache on day 4, alleviated with 2 sips of coffee that day.
As of today, I drink half a "Tall" every day, and feels enough. If it's too stressful, I also drink another half on the other half of the day, and these are my findings about my body.
Considering I'm not in "battle mode", I can really work well with half a mug of coffee/day.
Coffee shorts my hunger regulation and appetite, and makes me lean to sugar. That's not good. Considering my brain has less brakes and way higher idle than most people (per my doctor's words), this is double bad. So regulating coffee has a net positive effect on everything.
I can reliably build and reset coffee reliance/resistance now, since I know how my body reacts to caffeine.
I always think 10-12 hours ahead since it's caffeine's life in your body. Will I be awake 10 hours later, or will I be battling against caffeine to sleep? This is important for me.
Coffees with mild/mild-high caffeine concentrations works best for me. I don't like high-caffeine or ultra-caffeinated coffees. They make me tipsy causes heart palpitations and creates stress for no reason.
Black tea is a good aid for sustaining my focus. It improves focus, but doesn't create the same stress on my body. I can almost drink infinite amount of coffee until 2 hours before sleep, and it'll keep me collected and focused. What I live is it doesn't create an illusion of being not-tired by priming the body, so I can reliably feel how tired I am and plan accordingly.
Hope this helps, and please don't hesitate to ask for further specifics.