Everybody's body is different. You just have to keep experimenting. It's OK to go too far in every direction. Then you know where that is and have some idea of what a good compromise might be. I have my saddle clamp about 1/3 of the way from the front, using a 30mm setback seatpost. So I sit well back. That encourages the use of my glutes and hams, which I prefer. Not everyone does, not by a long shot. So yes, one's current best saddle fore-and-aft position is tricky to get right, partly because it affects how one pedals. When one changes how one pedals, it takes maybe a couple months of steady riding for one's neuromuscular system to adapt and get strong and efficient in the new position. A lot of people don't get that. It's not how it feels at first so much as how it feels after a week or so. That means that it's possible to adapt to many different positions. The question then becomes what's your personal most efficient or durable position? That's not a simple question. With appropriate exercise and training, it should be possible to stay in the saddle (with breaks every few hours of course) all day and all night, too, without any great suffering.

Whether the saddle slot goes through or not doesn't matter as far as comfort is concerned, though the width of the slot certainly does.