What happens if someone under 60 kg takes the higher dosage? Will the death be more violent?
How can one know for sure that you lose consciousness before dying, and not suffocate to death while conscious?
It's best to take the amount which is recommended. You may end up vomiting it all if you'll take more SN than written but vomiting can happen even using the recommended amount (even if used with antiemetics).
To be honest, we don't know. People who successfully ctb used these recommended numbers and I don't know a single person who used more than that, only who used less.
SN doesn't deprive the oxygen from your whole body but to individual cells within your body.
It changes your blood in the way so it can't carry the oxygen. You will still be able to breathe normally but your breathing can become deeper due to the fact that less oxygen is within your system, however it won't hurt.
I imagine if SN was that bad, people who failed wouldn't want to repeat it again and the medical reports on the internet should mention if the patient experienced suffocation feeling. If the oxygen is cut instantly, you only have few minutes to live (I've read death from hanging occurs in about 30mins, up to 1h in rare cases, while for SN it's 40mins - 4h) but SN is slowly depriving the cells of oxygen, not instantly.