For me, it has to be Leuchtturn1917's 120g/m³. Also like Rhodia, though it's a bit thin for my preference. Happy to hear you guys' suggestions for a slightly heavier (let's say 100g/m³ and above) paper, either loose leaf or in a notebook.
Very little in my experience, but if you use very heavy, staining inks, it might be an issue. For example, Noodler’s Baystate Blue will show through.