How slow and how fast things are as they relate to the different things put in place that determine how fast and how slow a task should be done is going to have to be very sound. Otherwise it will just turn out worse than what it was. I'll give an example with the chopping down trees.
If I'm just starting out in the game, I will have hardly any strength. I've just started so I'm not hungry, but I also haven't eaten anything that boosts my health and given me energy, such as things like leafy wild edibles, fruit and berries, meat from animals. Wild edibles will give the most nutrition and biggest energy boost, but will offer less fill. That way hunting serves a purpose of it's own in that you hunt for animals to get full, while plants, nuts, and berries all serve another purpose and have their place in the game. This will put a balance to things and in incentive to give attention to these these aspects of the game. So I've just started out. I have no tools. I'm full but no extra energy from eating plants. The fact that I have very little strength will be given the most weight when considering the speed it should take to chop down the tree. Then plants and other sources of energy hold another weight, less than character strength but more than condition and type of tool.
Let's say I'm just beginning the game. My strength is 10/100. It should take me 25 seconds to chop down a tree, 15 whacks. If I spend time eating edible plants, berries, nuts, taproots, fruit, then accordingly I will have more energy, which not only helps save time chopping down trees, but also boosts my ability to gain strength at a faster pace. Albeit, not very much faster, but fast enough to where you can notice a difference. You'd also have to factor in the rate at which your energy levels neutralize. They can't neutralize too fast or else it won't be worth the time invested in foraging plants, learning about which ones to eat, etc. But it can't be too slow either, or else strength points go up too quickly. But let's say you have a lot of energy prior to chopping a tree, or whatever grinding task is before you, you are going to be somewhere around 20 seconds. If my strength was 100 it would take me 3 seconds to chop a tree down, 5 whacks, which means faster animation. There should be 2 animations for tree chopping, one for below 50 strength and one for over 50 strength. Now let's say you have a 100 strength but are hungry and have no energy, it would take 10 seconds. You still want to keep healthy eating and taking care of your fatigue levels a priority in the game, in order to maximize the place cooks have in the game. Also, since it's energy from plants, without meals you have to cook and prepare for, you should get that energy boost but have it not last too long, while actual dishes give you energy boosts that last a very long time in comparison. That way cooking proper food and mixing it up has their place in the game, while hunting and fishing have their place, and edible raw foods and leafy greens have their place. And I could go on but I think I'll stop here.
The point with all of this is that while it might seem like splitting hairs with certain things, it will actually bring the game to life and make it extremely dynamic, not to mention incredibly unique, unlike any game out there. These little things create a very immersive feel to the game that would possibly even set it so far apart as to revolutionize not only RPG but the way for similar games to handle the inevitable grind that must take place if a game like this is to be well balanced and life like.
If you have better ideas, leave comments. If you want to challenge in a healthy way, to spark discussion, leave a comment. To me this very thing is the steak and potatoes of a game. It should be the central core focus of any type of game like this, and to the degree that it is properly worked out will be to the degree it becomes a game that separates itself from others.