Still waiting on a new kitchen scale to get weights for all my gear, so I don't really know yet. I've been trying to pare down my pack weight since its been a bit silly, but when looking after other people's kids I kind of feel its my job to be ready you know?
I would like to carry the absolute minimums, so far the BK-13 is the smallest and lightest knife I have that will do everything, but it doesn't have much of a handle. For that a SAK works better, and a Compact has everything, well, not a saw, so better a Farmer. But for just a couple grams more, the rucksack has a bigger blade, bigger saw and better handle. But handling wise, the rucksack needs two hands, but I can pocket tether my Izula, and now I have a one-handed knife, as well as all the tools I need. But I keep needing pliers for things, moving pots on the fire, grabbing lids, better also have the Skeletool. Its not just me relying on these tools, its also my clients, so I need to know they will work, no matter what, and Aussie hardwoods are tough to handle with a small knife, so lets bump the izula for an RC-3, Now I've got a big blade so I can reduce the Rucksack to a huntsman...... and it goes on and on and on. I suppose a guy could have worse problems.
If I wanted to, I'm sure I could get by just fine with an opinel #6. but what's the fun in that?
I'm sure once I have item weights for everything, I'll have a better idea of what I should carry and how many "backups" I can ditch. Its also a matter of figuring out exactly what I'm needing a knife for, and what characteristics it needs to have for that, and how to make the most efficient over-laps without getting silly redundant.
To answer the question, I've hiked with heavier knives, but now the heaviest I'd go for a single blade folder would be 3.75oz (full size griptillian) Or for a fixed 9oz (RC-3 with sheath) I don't see a need for more than that, considering I can get more blade for less weight with other knives, it makes sense to cap it there.