Ok, my ingredient bag is overflowing, so I guess it's time to spend an hour or so burning essences to craft useless shards. Currently, I'm about 20/20/20. When crafting just to earn crafting xp, what level of success do you aim for?

In other words, I usually just try to use recipes that have an 80 to 90% chance of success. But I remember reading someone's post a while ago that mentions they usually use recipes that have around a 50% chance of success. Obviously, the lower the chance of success, the fewer essences are used but the more likely the essences are to be wasted on a failed roll. Which do you recommend?